What do Persuasive Interrogators, Thoughtrender Lamia, Gray Merchant of Asphodel, and Cybermen Squadron all have in common?  Give up...?

Your opponents really don't want you to have four or five copies of one of them ETB/attack/die in the same turn.  The math gets... oppressive.  Welcome to the new Kardur...

So... it took me a while to figure out how best to abuse Kardur, Doomscourge, but the Aha! moment finally arrived.  I've been saving a foil copy of him since I opened packs on release night, knowing he had to be a general someday in the future.  I just couldn't figure out how to do it well enough to justify a build.  But, no longer.

Since it's way out of color for black and red to flicker cards, one must get creative.  Luckily, red provides ample options to copy creatures, putting token copies into play, which is all we need with Kardur (they die from the legendary rule, but still ETB and trigger).  Black provides ample options for recurring Kardur directly into play, often once each turn (ideally we don't want the card exiled and back to the CZ; staying in the grave is not a problem, as it can often provide an ETB every turn with the right cards (Feldon of the Third Path for one, or make a copy of Doomed Necromancer to bring Kardur back to play [no exiling]).  Stuff like Jaxis, the Troublemaker and Delina, Wild Mage make it easy to copy Kardur every turn (since Delina will effectively be attacking unblocked each turn after Kardur's first ETB trigger clears the path).  On top of that, you have some colorless cards to flicker Kardur with, like Conjurer's Closet, Golden Argosy, and Sword of Hearth and Home.  There are too many worthy options for copying/recurring/flickering Kardur (13 good ones that can get an ETB from Kardur every turn, plus more), so how many options of each you want in your deck is really up to you.

Since the backbone of this deck is copying Kardur, and/or repeatedly recurring creatures from the grave, we have a ton of options for triggers to abuse.  It's rare to get to abuse ETB triggers with black creatures (and red to a lesser degree), so some of those are pretty juicy to include (like Sidisi, Undead Vizier).  Making token copies with haste means you can abuse attack and combat damage triggers as well, and with sac outlets, you can ensure they also die during combat to trigger Kardur, as well as hit other death triggers.  Most of the options in the deck for copying creatures tie in an exiling of the creature to remove it, preventing death triggers from applying, so sac outlets are needed if you want to go that route (and who doesn't like nice sac abilities with crits that are going to leave anyway?).  Because the options are few that create tokens that actually die, the need for sac outlets is high if you want to abuse death triggers on various cards like Zulaport Cutthroat, which isn't necessary in the deck (it can be crazy strong without abusing a single non-Kardur death trigger), but it opens up a lot of options for big life loss to each opponent (albeit it's often ideal to kill/sac multiple creatures simultaneously, instead of one by one).  With something like Zulaport Cutthroat, if you make four copies and sac them one at a time your opponents will lose 14 life, whereas if those four token copies all died simultaneously they would lose 20 each (and you gain an equivalent amount of life).  The fun ones are triggers that grow exponentially for each copy in play, with stuff like Coercive Recruiter, Gemcutter Buccaneer, and Thoughtrender Lamia (copy it three times and each opponent discards nine cards) providing solid value when copied multiple times.  Kardur also provides ample opportunity for life-gain events, so life-gain triggers are likewise an option (Marauding Blight-Priest and Well of Lost Dreams are worthy, maybe Epicure of Blood as well).

Schematically speaking, this deck concept allows you to almost "break the game", in the sense that you get to achieve something which is very difficult to do with black in Commander: put/have multiple copies of a creature of your choice in play simultaneously in the same turn, and/or have multiple of the same creature all die in the same turn.  Card designers generally aren't planning for that, so when you get to do it with certain cards, things can get a little wild, making seemingly tame cards become powerhouses when copied (your opponents will love Cybermen Squadron... talk about a remove-on-sight card for this deck!).

One of the fun things about using Kardur, Doomscourge to make your opponents' creatures attack each turn is that it turns into a table equalizer, at least among your opponents.  If one of them is getting too strong, well, all their creatures are going to get tapped from attacking and leave them open to each other player's attack.  Whoever rises up above gets beat back down with ease by everyone else, if necessary, at least in terms of their life total.  And since each opponent is going to be tapped out (aside from any new creatures that couldn't attack), they're each fairly wide open to commander damage too, which can also speed up the game.  Forcing opponents' creatures to attack accelerates the game, especially after a full turn of Kardur's presence when they are attacking mostly unblocked.  And since you remain unattacked each turn, Planeswalkers are ideal to include.

Since Kardur triggers on opponents' creatures dying while attacking, it makes sense to gift our opponents creatures as fuel to that fire, which of course whittles down our opponents' life totals and gives us life.  For example, copy Nettling Nuisance a couple of times, then attack (unblocked) with all three (original and two copies) and gift each opponent three continuously goaded 4/2 tokens that can't block.  Another fun one is Life of the Party, where even though they're only getting one copy, it's a doozy, and they can get extra copies if Life of the Party recurs from the grave.  What's better than having your opponents kill each other off for you, using creatures you gave them?

One thing to remember is that the creatures in your grave are not gone, and are often quite easily brought back into play.  This matters when one objective of the deck is to copy certain creatures multiple times, as once one of those creatures is in your grave, you can recur/copy it into play and then copy it with your other cards, potentially winning the game.  Being in the grave just means one more instance of an ETB trigger when you recur it, before you start copying it, which can be a very good thing.  Your graveyard is truly an open resource with the right cards in play, or in your hand.

Strategically speaking, because attacking death triggers matter to Kardur (and lots of other cards care about death triggers), and most of the available cards to copy Kardur with end up exiling the token, it's best to use exiling copiers for Kardur or other legendary creatures that die on ETB, or on creatures you expect might die in combat when an opponent has viable blockers.  Try to save your copiers who sacrifice the token for nonlegendary creatures that won't die in combat, and/or tokens you won't be sacrificing simultaneously (like sacrificing multiple Zulaport Cutthroats to a Tar Fiend ETB).

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Ghired's Belligerence can be a game-winner.  Since we're typically giving small creatures to our opponents and/or ourselves, we have (creature) 'fuel' for Belligerence turning into creature deaths, which in turn translate into populate triggers (after we make a token copy of a specific creature).  That means it's well within reach to populate 5+ times by mid-game, where, say, five token copies (plus the original) of Devilish Valet could/should be a game-ender (five Valets swinging for 16 trample each, plus the original swinging for 32 trample, equals 112 trample damage).  Making five or six copies of Intellect Devourer is another fun way to flip the tables on the game, especially when those copies don't go away at the end of the turn.

Orthion, Hero of Lavabrink is worthy of inclusion from the first activated ability alone.  But that second one, that's game-winner territory with a lot of the cards in this deck.  It takes nine mana, but eventually, that will be available, and the game will be over.  All five tokens have haste and see each other ETB together, as well as die together, which opens a lot of doors for some serious fun with stuff like Gemcutter Buccaneer (30 treasure tokens), Zulaport Cutthroat (30+ life lost per opponent, you gain 30 life), Xathrid Necromancer (30+ 2/2 creature tokens), and Coercive Recruiter (gain control of your opponents' best 30 creatures UEOT).  Or maybe Nekusar, the Mindrazer has been making everyone draw a lot of cards... copy Thoughtrender Lamia five times... :)  Bye-bye 30 cards from each opponent's hand.  So yeah, Orthion can make things get wonky once you have the mana.

Nightmare Shepherd... the timing of Kardur dying to get copied with this either requires combat death (not likely with almost no blockers) or a sac outlet, and I'm not a fan of sacrificing him to get exiled and recast from the CZ, when better options to get his triggers should be around.  However, if Kardur were destroyed, I would happily exile it with the Shepherd and give him a second life before I have to cast him from the CZ again.  Nightmare Shepherd is great for catching any dying creature cards, as it allows you another chance to copy something juicy, and gives your nontoken creature a bored wipe safety net.  Kinzu of the Bleak Coven effectively does the same thing, and Dollhouse of Horrors is the activated ability version, which has its benefits.

Twinflame is probably better than you think in here.  Yes, it can copy Kardur, and make copies of multiple different creatures, for a cost, but where the hidden value comes through is when you're trying to create a bunch of copies of the same creature.  After you use other cards to copy the desired creature a number of times, then you cast Twinflame to copy the token copies, effectively doubling up as many as you can pay for.  It's not cheap to do, but mid/late game it could be a potential game-ender for 5 or 8 mana.  Early in the game, Twinflame is a cheap/easy way to copy Kardur, and as the game goes on its potential value only increases until it becomes a game-winner (with the right creature[s] in play).

You can exile/imprint Kardur, Doomscourge with Mimic Vat as long as you have access to an activated ability that can make a token copy of a legendary creature under your control, or have instant speed creature destruction, or an activated creature sac outlet.  If someone tries to remove Mimic Vat while it has Kardur exiled and imprinted, you respond at instant speed by making a creature hit the grave so that the Vat will trigger to let you exile that creature, and then put Kardur in your graveyard, which you reroute to the command zone.  The ol' switcheroo... 

Mirror-Style Master is pretty fun... the original copy puts a +1/+1 counter on Kardur, and Kardur attacks and makes a copy of itself triggering the goads.  Next make a couple token copies of Mirror-Style Master and the new copies ETB and put two more +1/+1 counters on two more creatures, gaining M-S.Master's abilities.  Then attack, and each attacking copy makes copies of each attacking modified creature, including Kardur.  The more modified creatures you can attack with, and the more copies of M-S.Master you can attack with, the bigger the army you create, while probably making a ton of triggered events go off, that might win the game in itself.

Dutiful Replicator is a must-have, as it makes token copies that don't go away.  When you can make copies of two different creatures, make a copy of the one you want to keep, then make a copy of Dutiful Replicator, which copies the other token copy, and now you have two copies of the first creature, using two copy effects, but one of them you get to keep (plus a copy of the Replicator for an attack).  This is great with stuff like Mirror-Style Master, Caves of Chaos Adventure, Champion of Dusk, etc, making both multiple copies to benefit from now, and permanent copies to benefit from on future turns.  BUT the big one is copying creatures that let you copy creatures... each turn you get to make more and more of them, if you want, as all you have to do is copy one first, then repeatedly copy the Replicator, making copies of the first token... each turn you nearly double the total if desired.

Kindred Charge isn't for Kardur, but for when you need a lot of copies of one creature with an ETB or combat trigger (the copies are exiled, so no death triggers).  Make copies of it the old-fashioned way, with other cards, then cast Kindred Charge and double the total number of those creature tokens (and maybe others).  Six mana to go from three to six copies of the creatures is usually worth it.  Going from four to eight is definitely worth it!  Hello Gray Merchant of Asphodel!  All that being said, because there are so many ways to make token copies of creatures, I think this is a borderline include/exclude... it requires a lot of things to happen before combat, and while that's possible, it's not a high likelihood to happen as often as some other combos in the deck.  I'm putting it in, but it's cost and limited scope/flexibility are reasons to think twice about it.

Cybermen Squadron is bonkers in this deck... while some cards in the deck go exponential with "squared" math, C.Squadron goes exponential with nearly "cubed" math, because each copy you make not only has myriad, but each copy gives each other copy myriad, and they stack.  With three opponents, one Squadron will dole out 15 total damage, with a 5/5 going to each.  With two Squadrons (only one copy), each will have double myriad, which means 30 total damage from each Squadron, and 60 damage total from both!  And with three Squadrons (two copies), each has triple myriad and doles out 45 total damage each, for 135 combined damage.  Four Squadrons (three copies) make 240 damage.  I'm gonna go out on a limb right here and say that the 7cc is probably worth it.  lol

Life of the Party isn't the most ideal copy target, in the sense that you opponents won't get to create more copies as well, but, I mean, it's still worth copying... especially if you have enough creatures in play already.  While it's not a good copy target, it is a good recursion target, and certainly worthy of using such cards if they're not needed for Kardur.

Archpriest of Shadows is great in this deck, because when you make a copy of it and Backup another creature, both of those creatures can recur a creature from your grave, and those recurred crits don't go away at the end of the turn.  It's primarily intended to keep Kardur entering play each turn, but with the added bonus of an extra creature as well.  With Kardur goading opponents' crits every turn, the attacks should go mostly unblocked, letting these guys go through and trigger, and if they are blocked, well, they have deathtouch... could be worse.

Geode Golem is a no-brainer here... just add a sac outlet so Kardur is in the CZ before you go to combat, then you have your ETB trigger each turn, and you can use your creature-copying effects on other funner targets.

Uchuulon is currently an underappreciated card for black... it clears creatures out of your opponents' graves, and effectively, for each creature you exile like this you get to make a token copy of Uchuulon, whose power is (greater than or) equal to the number of copies you have.  With a deck built to make opponents' creatures kill each other quite a bit, there should be enough crits in their graves to fuel lots of copies of Uchuulon, growing exponentially until they run out of creatures.  And if enough creatures are in graveyards, make copies of Uchuulon after you cast it, so each temporary copy will make a permanent copy of itself, jumpstarting their collective growth.  And with no blockers from Kardur, that could make for a quick game... at the end of the third turn after casting Uchuulon (without copying it), you should have eight 8/4 Uchuulons (including original).  And if you had copied it twice after casting it you would have sixteen 16/4 Uchuulons (assuming enough creatures were in their graves, which often won't be the case, but you get the point)... except oh yeah, the game ended last turn with eight (likely unblocked) 8/4 Uchuulons.  If you can cast it and copy it three times, the turn after next you are attacking with ten 10/4's.  So yeah, it's potentially a game-ending card in mid/late game, once graveyards have acquired enough creatures to exile.

Fiendish Duo is a dangerous card... if it's not countered, it's probably game over if your opponents don't have any blockers or removal.  If you have three in play, and all are attacking, they're swinging for 40 damage each, and 2/2 creatures swing for 16 damage.  It's too easy to make two copies of it... just cross your fingers it doesn't get countered.

Volatile Claws is a neaky good card in this deck, as not only do we plan to be attacking unblocked a lot, but we also hope to mass copy various creatures, many of which care about the creature types of other creatures you control (like Shepherd of Rot).  Maskwood Nexus does similar, and even provides extra creatures to attack with or sac to an outlet if needed.  Maskwood should only be included if enough cards in the deck care about creature types, which will depend on how you ultimately choose to build your deck.  Volatile claws at least provides the potential of a game-winning amount of extra damage in combat, but typically I prefer cards that do the same, but let me choose any player, just in case an opponent is primed to take out one or two other players if I boost their creatures... assuming I can attack them the next turn and win.

I didn't give Genasi Enforcers enough credit when I first looked it over for this deck.  Luckily I came across it again and thought deeper because I think it's sneaky good.  It'll take some freed-up mana to abuse, but if you have it, you can add up some serious damage.  Let's say we create three copies, giving us four total Enforcers, they attack and create their myriad copies, giving us four Enforcer copies attacking each opponent, then we pump them with six mana... each opponent will take 16 damage, or 20 damage each with eight mana.  That's a game-changing attack, and possibly a win.  If you only make two copies, and only pump four mana, that's still 9 damage per opponent, which is both a very realistic scenario, and respectable for a two-drop creature.  But the more copies you can make, the better, as it's effectively creating value for your mana spent.

Goblin Rabblemaster also gets going pretty good.  Attack with the original and three copies, and you now have four 10/2's and four 1/1's, delivering 44 total damage.  Four copies total 65 damage, and making two copies still delivers 27 damage.  And then the next turn you'll be swinging for even more, as your Goblin tokens add up.

Krenko's Buzzcrusher is an interesting option to include... early on it will let you limit the dual/triple lands in play, albeit they get to search for a basic land and color fix, but you limit their overall options with each copy you make.  And if you do it enough, they might run out of basics to search for.  Against 3+ color decks this could be quite impactful to play and keep copying.  But even if you only cast it once and never copy it, that first use is probably still going to be worth it, and then you have this handy little 4/4 flying trample to swing with.  And that shouldn't be forgotten... with each copy, you are likely also swinging for 4 damage as part of the package deal.

Tar Fiend is a creative way to get death triggers from token copies that would normally get exiled at the end of the turn, and even better, they all trigger at the same time, which matters for a lot of cards like Undead Auger.  Just make sure it's the last token copy to be created on your turn so you can sac all the others to it.  It's best to try and time it after an attack, but circumstances dictate what will make the most sense, as it might be necessary to have it enter on an attack trigger, making you sacrifice other tokens before they can deal combat damage.

Invasion of Ravnica // Guildpact Paragon is a nice card in here because, on top of the permanent removal, it's easy to defeat under Kardur's reign of terror (like any other battle), and once flipped you have a fun creature to copy if/when you have a two-color spell to cast.  Having multiple copies of Guildpact Paragon in play puts a lot of good cards in your hand because, with each copy in play, you are increasing the chances of finding another cheap two-color spell to cast next, and then trigger them all again.  This means it is best to abuse when you have enough extra mana to spend, and ideally when you can create two or three extra copies of the Paragon, likely grabbing you multiple two-color spells from the top 18-24 cards with each spell cast.  And just a quick reminder, two-color cards are typically more powerful/efficient.  On top of that the Paragons are 5/5 beating sticks, so it's a pretty fun little package.  Permanent removal; 5/5 beaters; cast and "draw" a lot of two-color spells... why not?

Golden Argosy is another sneaky good card, allowing you to delay-flicker Kardur, which is good enough for his trigger, as well as any other creatures you feel have a bigger ETB value than their attack damage value, and are not going to be copied multiple times for an exponential buildup of triggers.  Even though Argosy's crew is only 1, you can still crew it with as many creatures as you want, which adds a ton of potential value beyond Kardur.

Populate won't help Kardur unless you've made a nonlegendary copy, but the available cards for black and red are quite handy in this deck.  Promise of Aclazotz lets you sacrifice a token that would otherwise die, and make a copy of another token for keeps... which would be handy if Kardur exists in play as a nonlegendary token.  Determined Iteration doesn't let you keep the token, but it's another token copy when you're trying to stack up an exponential trigger (which gets sacrificed instead of exiled).  Ghired's Belligerence can wipe out a lot of 1/1 creatures (yours included if needed), populating each time, which makes it super strong, as there aren't many cards in red and black that let you make/keep token copies.

On that note, Ghired's Belligerence and Promise of Aclazotz are two of those such ways to create token copies that you can keep.  You can also do it with Dutiful Replicator, Helm of the Host, Lithoform Engine, and Mirrorpool, then Sundial of the Infinite can end the turn after your "end of the turn" sacrifice/exile triggers go on the stack, wiping them clean and allowing you to keep your creatures... if you can tutor for an artifact, Sundial is worth be the target.  Plus it can untap Kiki-Jiki, Mirror Breaker, Orthion, Hero of Lavabrink, or Jaxis, the Troublemaker.  Nightmare Shepherd, Kinzu of the Bleak Cover, and Dollhouse of Horrors also make copies you can keep, but at the cost of exiling the original... it's like getting a completely free and paid Assemble the Parts whenever one of your nontoken creatures dies.

Persuasive Interrogators is another sneaky good card, as each copy triggers for each Clue you sacrifice.  Make three copies, giving you four clues total (including from the original), and sacrifice each clue (yes, it'll cost 8 mana) triggering each Interrogator... that's 16 triggers that give two poison counters each, for 32 total poison counters.  Give 12 to each of two players, with 8 left over for the third play, assuming three opponents.  Two are dead, the other dies the next turn if they can't get rid of your original Interrogator (copy it one next turn, sac the Clue for four poison counters).  Even if you can only make two copies, that's three Clues, six mana, and nine triggers, for 18 poison counters, 12 to one, six to another.  Next turn you do it again, game over.  Fun card; sneaky good.

Marionette Master is an interesting one, that, like many of the cards in this deck, prospers when multiple copies come into play.  The original copy should enter with three +1/+1 counters on it, so you have a (big, sustainable) creature to copy that can pump some damage.  After that, pending how many copies you can make, you might want to give a copy three counters as well, but the rest should make 1/1 crits that can be killed/sacrificed to trigger each of your copies.  Mathematically speaking, if you can only create three or fewer copies, then have them all make 1/1 creature tokens; making three copies, with 9x 1/1 tokens, will force 63 total life lost when those tokens all die.  If you can create four or more, have one copy get three +1/+1 counters, and the rest make creatures.  With four copies, and only two making six 1/1 crits, when you sac the 1/1s you'll generate 99 total life lost, and 144 life lost if you make five copies with nine 1/1 tokens to sacrifice.  Making just one copy can still force 15 life lost.  If you can only make two copies, have them make six 1/1 tokens, then instead of sacrificing them (for 36 life lost), wait a turn, then with your two copies make three more tokens (nine total), and put three counters on the other, then sac all the 1/1 tokens to deal 81 damage, instead of 36=36=72.  Just for the sake of argument, doing the math, once you can create seven token copies at once, it then makes sense to have two copies enter with three +1/+1 counters, then when you sac the 15x 1/1 tokens you force 255 life loss, versus 252 if you only had one enter with the extra counters.  Of course, at this point, we're in rare game territory, both in being able to create seven copies at once and in having anyone with enough life left to necessitate the game going this far.  But you never know, and now you know how to handle it if it happens.  As I said, it's an interesting card, as the mathematical possibilities create potential inefficiencies if you aren't paying close attention, but the payoff is pretty big for each copy you can make, no matter how you do it, so long as the original is a 4/6 thumper.  Also, this requires a deck build that has lots of sac outlets in it, which I think is more than justified.  Too many good cards trigger on death not to include a nice range of sac outlets.

Port Razer goes infinite with anything that triggers on attack to create a copy of an attacking creature, which are plenty in the deck.  Each combat create a new attacking copy that can deal combat damage

Slicer, Hired Muscle // Slicer, High-Speed Antagonist isn't so much a copy target, but is still great with Kardur, effectively swinging for 6 damage on each player's turn, or up to 24 total damage a round with three opponents.  You choose who gets to attack with it, limiting its risk of dying, and it comes back at the end of each turn.  If you convert/flip it, it should be easy enough to get a combat damage trigger through and convert it back to the front side on your next turn.

Blitzwing, Cruel Tormentor // Blitzwing, Adaptive Assailant is another Transformer that fits the deck, as it will be easy to attack one player mostly unblocked and deal a heap of damage that Blitzwing will double, and likely, they die.  Next turn, next player.  It flips during combat on your turn, likely using flying for evasion if blockers are present, so it should be able to get some work done pretty fast.  Cast it for its MTMtE cost, getting it into play a couple of turns sooner, then it can attack and flip the next turn, and boom, you're off the rac... no, you're off to the graveyard, with/for your opponents' dead decks.

It's worth noting that successfully triggering Kardur each turn means you never get attacked, which means monarch and initiative triggers are worth consideration since you're likely to retain them with relative ease.  Court of Ambition, Court of Embereth, Caves of Chaos Adventurer, Ravenloft Adventurer, Crown of Gondor, etc, are all worth consideration.

Hoard Hauler is another sneaky good card, as it's easy to turn it into a creature and then copy it, and each copy attacks the player with the most artifacts in play.  Boom!  An explosion of riches is likely to befall you, especially if they're loaded on artifact tokens and have no viable blockers... or maybe they just play Urza with an artifact overload.  Plus it's a 5/5 and only a 4-drop.  That's all-star material!

Smuggler's Buggy is another great vehicle to crew and copy.  Each copy lets you cast one out of four cards for free, and since they typically enter attacking or with haste, you're likely to get each copy to trigger on combat damage with at least one opponent unguarded; if too many blockers exist, then copy a different creature.  But that's some serious value!  One out of four cards should be worth playing, and it's much preferred to be casting cards off the top of your own deck than someone else's deck.  And like Hoard Hauler, it's a 5/5 4-drop, so you're getting great value out of each copy you make.  (Compare to Weatherlight.)

Strixhaven Stadium is almost unfair in the deck, but what's even more fair is using something like Lithoform Engine to copy the last ability and take two opponents out at once.  Bam Bam!  The combat triggers go onto the stack and resolve in whichever order you choose, and as the 10th counter is put on and resolves, you copy the trigger.  Bam Bam!

Larceny... buahahahah!!!  Okay, enough said.  And it's like a $0.50 card...  Have fun!

Turf War lets you steal a land of your choice from each opponent, assuming you can get combat damage through, and then with Kardur creating a combat shield, you're not likely to give those back for a while.  That means stealing opponents' best lands for you (Nykthos, Shrine to Nyx, etc), or the best lands for them ([[, which might mean removing a combo piece or a similar worthy target.

Torgaar, Famine Incarnate is a fun sac outlet, as it provides a cheap 2cc way to sacrifice a bunch of creatures simultaneously (as many as you want, not just three), and then turns into a copy target for a potentially devastating ETB trigger, especially versus a life gain deck.  While providing a similar sac outlet purpose, Dargo, the Shipwrecker is a borderline include, as he's effectively just a 1-drop 7/5 trample sac outlet, which, there are worse creatures to copy, if desperate.  Last-Ditch Effort also does the same but with a damage thump.

Ogre Chitterlord would be a great card in this deck if the 1/1's had haste.  The way I'm building it, I don't have enough need to add cards that give creatures haste, so Chitterlord turns into a two-turn card... first turn creates the Rats, second turn gives those Rats +2/+0 for each Chitterlord.  But that can still do a lot!  Copy Chitterlord twice and attack with all three copies, and you put 10 1/1 Rats into play, on top of the other two from the original's ETB, for 12 total.  Next turn copy Chitterlord twice and attack with everything and you now have three 6/5's and 12 7/1's swinging for 102 total damage.  That's very respectable for only being able to make two copies, even if it requires two turns to accomplish.  And even if Chitterlord is removed before the second turn, you still got 12x 1/1 Rats out of it and got to swing with two 6/5's.

Grief pairs up well with Kiki-Jiki, Mirror Breaker and Feldon of the Third Path, etc, providing you instant speed removal of cards from an opponent's hand after they draw it, assuming you can get priority before they cast it.  It's not a crazy max-value card in the deck (compare to Junji, the Midnight Sky and Thoughtrender Lamia), but probably provides value in the ability to choose the discarded cards.  Those three, plus a few wee ones like Burglar Rat, Elderfang Disciple, or Elvish Doomsayer, and you can see a path to some serious and fairly consistent hand control and card advantage.  It's tempting to forego letting opponents cast lots of creatures and kill each other, and instead push hard to force discards and limit what they have access to... it could be much worse than having all your opponents constantly top-decking.

On the idea of Junji, the Midnight Sky, where a copy dies when it ETBs due to the legendary rule, it makes the death trigger immediate and easy to access.  In a similar vein, Atsushi, the Blazing Sky is similarly powerful and diverse/flexible... being able to make three treasures from one copy is quite strong, especially without requiring an exponential/stacked trigger, then copy again and exile cards to cast, then make more treasures if needed, etc.  These are great targets if you can only make one copy after triggering Kardur.  Tuktuk the Explorer is nice because it's cheaper and easier to get into play early, but still provides a solid 5/5 token payoff. 

God-Eternal Bontu provides a different shenanigan in a similar way, where copying it allows you to sacrifice the original, keep the token in play (probably until end of turn), and put the original card three down in your library, allowing you to cast it again and draw more cards, making him a very handy sac-outlet draw-engine, albeit for the cost of five mana per cast, but you also get to copy it before casting it again, so two ETB triggers and one death trigger.  But that's great value for the number of cards you're drawing!  But there's more... because you're getting a simultaneous ETB trigger from the token and death trigger from the real card, you get to order them as you choose, allowing you to put Bontu into your deck third from the top, then draw him into your hand if you sacrifice two creatures and draw a card from the copy dying (from Jaxis' trigger).  Cast or copy it every turn to clear the field of token copies in play, potentially getting a card with an appropriate death trigger to stack and go exponential from a bunch simultaneously dying (Butcher of Malakir).

Vile Entomber gets Dread Return (a nice [free] way to sac and death-trigger multiple crits simultaneously), which gets another creature from your graveyard back into play (tutored by copying Vile Entomber), which might be a Whisper, Blood Liturgist (sac outlet) or Feldon of the Third Path, which can now retrieve whichever creatures Vile Entomber puts in your grave each time you copy it, which basically means there's a timer ticking until you win from copying such a card multiple times.  Wake to Slaughter is a secondary option, if desired, and Crawl from the Cellar does similar enough.  Corpse Connoisseur, Gravebreaker Lamia, and Burning-Rune Demon are redundancy, and Sidisi, Undead Vizier tutors without using the grave.  Yes, Demonic Tutor and [Vampiric Tutor]], etc, are much more efficient tutors, but being able to copy and tutor multiple times is kinda fun.  This isn't a fast deck, per se, but it's always building toward a swift wincon.

Spike Cannibal is a fun lil guy, albeit we're generally not too concerned with opponents' creatures being big.  But eventually, it will be 1v1, and then ol' Cannibalistic Spikey can potentially do some crowd control, beefing him up to be a one-punch win with opponents' crits are all tapped from attacking.  He just adds another dimension of control to the deck, and worst-case scenario, he might be a game-changer if an opponent is popping off.

Akki Battle Squad makes infinite combat phases in this deck, so long as you can make a copy of it during each attack phase, BUT it requires your creatures to be modified so they can untap and attack each combat, which is not something this deck does easily.  Take that for what you will.  Maybe you can scheme up a version where this fits...?