This is a rotation proof dimir control deck utilizing a small rogue package centered around Thieves' Guild Enforcer and a bunch of removal and counter spells. I've lately come to enjoy torturing my opponents by denying them their broken plays - especially towards the end of the now "old" standard 2020. While this deck is not as oppressive as a pure blue counter "everything" deck, it can come back when the opponent is able to deploy something on the field - something pure blue can struggle with at points.

Main Strategy

In the end we want to beat our opponents up with our fairly small creatures while denying them their plays and make their life miserable. Our three main mechanics for that are flash, mill, and interaction.

A good majority of the spells in the deck that can be played on the opponent's turn. That makes it way easier to react appropriately to the opponent's plays. Be it countering dangerous plays, removing threads from their board or building up our own board presence. Often we only need our turn to play a land and attack with our creatures.

The second main focal point of the dedk is interaction with the opponent. That interaction is mostly preventing opponent's plays through the use of our counter spells or getting rid of the opponent's board presence - that snuck past our counters - with our plethora of removal spells.

The third, and only minor theme, sort of also plays into the "removal" and "denial" aspects: Milling. This is only a really light theme of the deck as we don't want to mill out our opponent's but have their cards wasted away in their graveyard while also boosting the effects of our cards in return.

The Cards

The core of our deck is our rogue package. I've already been playing dimir flash as a preparation for the new standard before core set 2021 introduced Thieves' Guild Enforcer. That's a fine little one-drop and the heart of our rogue package! That package consists of only three different rogues, but each as a four-off: Thieves' Guild Enforcer, Brazen Borrower, and Cunning Nightbonder. Together with the other rogues the enforcer is a little mill engine that can stop the opponent's creatures in their tracks during the later game by gaining deathtouch. Multiple enforcers on the filed can mill like crazy! Brazen Borrower, as always, is a strong card being a bounce effect on a stick with a decent evasive body. Him being a rogue is just a cherry on top! While Cunning Nightbonder's second effect to reduce flash costs is not that prevalent in our deck - yet still helpful -, its other properties make it a worthwhile inclusion: In counter mirror matches having un-counterable plays due to the Nightbonder's static ability is a huge difference for the player who resolves this one first. Also it's a rogue for milling with the enforcer.

Besides our rogue package we have a small set of additional creatures. Slitherwisp is an obvious inclusion. It's an engine in itself - draining the opponent for life and netting us card draw! But due to its strict mana requirements we're only playing three instead of a full playset. A random Lochmere Serpent is a decent mid to late game finisher (had him played with the Cunning Nightbonder's help on turn 4 once!) that's also hard to get rid of: It can be unblockable, can draw cards, and return itself from the graveyard to the hand. The oddest one in the bunch is Overwhelmed Apprentice: That little one mana wizard helps us mill the opponent and setup future draws by scrying when it enters the battlefield. I chose it over Merfolk Secretkeeper because it's overall cheaper to play (one mana in total instead of two - so, an additional creature on turn one), it has a non-zero attack value making it more effective versus opposing little creatures, and helps smoothing out our draws. While it mills less cards the amount milled is still enough for the early game. And later in the game the scrying effect becomes the more important thing.

Now for the non-creature spells. There are eighteen of them. And only eleven are counter spells. Seems moderate! We are currently living in a creature based meta game, so we can justify playing two Essence Scatter in the main board. A couple of the generic counter Didn't Say Please (I'm loving the name of that card!) helps with our mill plan and therefore enabling the Thieves' Guild Enforcers true potential. Rewind lets us cheat on mana and double spell in turns where we shouldn't be able to. However, three of them is enough. Drown in the Loch is a very flavourful card drowning the opponent's spells in the deepness of their filled graveyard. Because we have six one mana mill cards this two-in-one generic counter and creature removal spell is in most games already enabled by turn two and only becomes stronger as the game continues! Having a cost that does not require two mana of the same colour also helps tremendously as we currently have pretty precarious mana bases with "tapped only multi color lands".

The pair of Extinction Events are our hail marys coming into play when we should loose control of the game. Due to the Nightbonder Omen of the Sea is often a one mana "scry two draw one" effect, a better Opt if you will. Combine it with Slitherwisp and you are drawing two cards. Not a bad deal! Cling to Dust is a fine little cantrip to get rid of the opponent's Uro, Titan of Nature's Wrath and targets for other effects, like Elspeth Conquers Death and the like. And that can be pretty important, since we are filling up our opponent's graveyard quite nicely. While the escape costs for Cling are quite steep they are still a worthwile mana sink in the late game and can help shrink the Enforcers of the opponent in mirror matches.

Teferi, Master of Time is a random one-off that's currently in trial mode in the deck. It can speed up filtering and make the opponent deal with him instead of us. So, yay Teferi!

The mana base is not that great due to the lack of untapped dual color lands in the format. So, we have a playset of Temple of Deceit (smoothing out our draws), two Dismal Blackwater (which should be Zagoth Triomes instead, but waiting for Zendikar first), a Castle Vantress (occasional smoothing), a Castle Locthwain (occasional draws), and two Fabled Passages. We also play more Islands than swamps due to have a more spells requiring double blue mana than double black.

Honorable Mentions

While Sea-Dasher Octopus is a great card it somehow didn't fit into the deck. We generally would want to play it for it's mutate cost, but our early creatures are all humans. I'd also like to rather play it with a creature set that either has larger bodies or more evasion. You can try to replace the Omen of the Sea and/or Lochmere Serpent with this.

Eliminate  and Heartless Act are decent spot removal. However, in this deck Drown in the Loch is strictly better.

Ashiok's Erasure would be a decent counter. However, there is currently too much Gemrazer around for it to be viable enough. Rewind seems like the better option.

I tried Whirlwind Denial against adventure decks. It could stop the cast triggers of Lucky Clover and Edgewall Inkeeper. Didn't do a thing to hold them off. Had them always at the wrong time. And in the late game that card is just a dead draw.

Some people might be missing Shark Typhoon. It's a good card, but I'm not really a fan of it. Contrary, I do like Voracious Greatshark. It's made cheaper by the Nightbonder, but didn't really fit into the style of deck.

Vantress Gargoyle fits more in decks with the main focus on milling the opponent to serve as a secondary win condition. Maybe I'll give it a try at some point. But I'm not yet there.