This is a deck I built for someone on Fiverr. If you want ideas turned into a deck, you can find me on Fiverr as Genoslugcs.

The Deck

I can see where you ran into issues building this deck. The main creatures Cavalier of Night, Cavalier of Thorns, and Cavalier of Flame all have similar abilities but don't point you in a clear direction for how to build around them. That said, I think I cracked the code.

First, they all mention the graveyard. So, that's a given. And we're going to make use of that with a knight reanimation package. Every creature in the deck (except for one) is a knight. Some are elemental knights, some are human knights, and some are zombie knights... But they all count as knights. So, let me introduce you to Haakon, Stromgald Scourge.

He will let you cast knights from your graveyard whenever he's in play. The only catch is that you can only cast him from your graveyard. Now we have a clear plan - Get knights (including Haakon, Stromgald Scourge) into our graveyard, cast them over and over, get nasty effects, and win through value and neverending attackers. This also fits the theme because nothing stays dead for long in Dark Souls. Now, how do we make this plan happen?

Fill the Graveyard

The cards above are the main ways to fill up the graveyard with cards quickly. Keep in mind that Haakon, Stromgald Scourge is the main one you want in the graveyard, as he can't be cast from your hand. So, if you see him with a Grisly Salvage, bin him for sure. Other cards like Cavalier of Thorns, Cavalier of Flame, and Bone Shards can also help put cards in the graveyard. Beyond that, your knights will likely die and naturally wind up where you want them.

Note: Stinkweed Imp and dredge can be confusing if you've never used it... So, let me know if I should explain how it works.

Sometimes, you'll end up with too many lands in the graveyard for your liking. So, I included one little safety net in Conduit of Worlds. It can give you access to lands that would be otherwise trapped and can also reanimate things if you don't have other spells to cast.

The Knights

It was important to me to A. Make sure the deck has a cohesive theme, and B. Make sure the deck plays cards that are good all by themselves, even at the worst of times. On the lower end of the curve, we have Foulmire Knight and Mosswood Dreadknight, both of which have adventure spells that can draw you cards and good bodies.

Next, we have three Corpse Knight, which gives you some damage to close out games even without attacking. And no, we're not playing white... More on this later. There are a full four Murderous Rider, as it's too good not to play. You can't beat a removal spell and a 3/2 with lifelink all on one card.

Then there is a single copy of both Ashenmoor Liege and Elite Headhunter. The Liege gives all your black creatures +1/+1 and does the same for your red creatures. So, Elite Headhunter will get +2/+2, making it a 4/5 with menace! Both of these cards help give the deck a bit more closing power at times. However, they aren't something you always want or in multiples. So, we have only one each. Remember, if they hit the graveyard, you can probably cast them from there.

Then, at the top of the curve, of course, you have the Cavalier package. These were great in testing. They have abilities that work very well with this shell I've created and are significant threats.

Removal And Interaction

You'll need to deal with what everyone else is doing as well. That said, the deck needs its creatures and requires them to be knights. Cavalier of Flame, Cavalier of Night, and Murderous Rider can all remove creatures, so that's a great start.

You also have Bone Shards, which can take out lots of threats and discard Haakon, Stromgald Scourge if he gets stuck in your hand. Lastly, there is one Bonfire of the Damned, which is here for that Dark Souls flavor! I couldn't not include it here. That said, if you can cast it for the miracle cost (or late in the game), it's a game-ending card. That's a total of 11 removal spells all pulling double duty in some way.

Foulmire Knight and Stinkweed Imp can also kill anything they block. Haha I didn't even realize how much this fit that "everything will kill you no matter how small" feel of the Souls games until now.:)

The Mana Base

The deck plays 24 lands in total, which I like. The mana base is also another reason we're on this "all knights" plan. Cavalier of Night, Cavalier of Thorns, and Cavalier of Flame have some pretty hard mana requirements to meet on a budget. But we hack the system playing all knights because now we have access to four Unclaimed Territory and Secluded Courtyard, which can cast all of the above - Green, Red, or Black all for a few bucks. This is also how you cast Corpse Knight with no white lands.

Next, the thing I wanted to mention is the hybrid mana on Ashenmoor Liege and Elite Headhunter. Having them able to be cast for black or red means that aside from the Unclaimed Territory and Secluded Courtyard, we can pretty much play a mainly black mana base. That said, you've got plenty of dual lands and a full four Savage Lands.

Oh, and the scry on the Temple of Malice and Malady help a lot with setting up Bonefire of the Danmed.