Assassin or Horror?

[Cyberium]

Namely, Etrata, Deadly Fugitive or Captain N'ghathrod.

Etrata:

1) Potentially create multiple colorless creatures per turn, from different players.
2) Can turn ANY of your face-down morph creature face-up for a flat cost, even if she didn't create it.
3) Can turn non-creature morphs face-up to "cast" it. Again, for a flat cost.

Captain:

1) Steals a creature or artifact without additional cost, from one player.
2) Provide Horrors with ways to avoid blockers and trigger milling.
3) Having the option to steal via milling, without the need to attack.

[yeti1069]

I think Assassins are a better tribe than horrors--lower CMC overall, more strong utility cards (removal, card draw), and often have some of their own evasion built in. I also think that a quasi-floor of hitting 3 opponents for damage and making 3 2/2s that may have some further upside is pretty solid. Having the occasional option to also then pay for a bomb is pretty cool.

That said, Captain works on different axes--it fits into a mill-centric strategy, attacking from a very different direction than most decks/players are prepared to address. The ability to steal cards without going to combat is VERY relevant, as a gummed up board making attacks difficult is somewhat common in EDH. The bomby horrors are bombier than the bomby assassins. Effects like that of Roaming Throne that act as a sort of force multiplier work for both, but doubling mill from ALL your damage dealers and then stealing an additional card I think is probably more valuable than getting a second set of 2/2s, but that's a close one. For me, the last part is that Etrata is going to lean into becoming a go-wide aggro deck, I think, since you'll likely get to the point of simply having a bunch of 2/2s with which you'll have nothing else to do, though Dimir is not a good color combo for supporting that kind of strategy, and I feel like, if going wide with 2/2s is where you want to be, there are simply better colors and commanders for that. Four mana to make any more use out of the cards you get isn't a ton, but it's also not a pittance, and you're likely to be restricted to only one activation per turn cycle until late in the game.

I could see throwing in Arcane Adaptation to turn your morphs into assassins to start growing exponentially, which is cool, but I feel like it would get old kind of fast. Captain feels fairly different from game to game.

[Cyberium]

The ability to steal cards without going to combat is VERY relevant, as a gummed up board making attacks difficult is somewhat common in EDH.

That is true... and I hesitate to think about using Training Grounds for Etrata just to reduce flip costs.

Though, while N'gthathrod can hit or miss on the steals, Etrata always gets something back. I wonder if we could make use of the 2/2s with some sac outlets. (Or just plain ol' Skullclamp + Attacking)

[Mookie]

There are 69 UB assassins, and 225 horrors. Neither has much typal support - assassins have a couple of legendary lords involving hit counters (Etrata, the Silencer + Mari, the Killing Quill), while horrors have a few cards from the precon. If you really want to lean into the creature type, horrors have a deeper card pool and tend to be slightly more expensive, while I suspect most assassin decks will look roughly the same. Of course Arcane Adaptation / Conspiracy open up a lot of options.

Ignoring the creature type and considering Etrata, Deadly Fugitive vs Captain N'ghathrod... Etrata is cheaper and is sweet with manifest / cloak / morph synergies. There are some fun things you can do with Scroll of Fate and other manifest effects to cheat stuff out. Meanwhile, the Captain works with any form of mill, which, again, has a much deeper card pool. You can get multiple things off Etrata though, while the Captain only gives one thing (assuming you even milled anything).

Personally, I would lean towards horrors due to there being more deckbuilding options. I also think that paying to flip things up with Etrata sounds sort of clunky (and you miss on ETB triggers). I'm not particularly a fan of morph though - if Etrata speaks to you or if there is an assassin you particularly want to play with, then go for it.

[yeti1069]

Personally, I would lean towards horrors due to there being more deckbuilding options. I also think that paying to flip things up with Etrata sounds sort of clunky (and you miss on ETB triggers). I'm not particularly a fan of morph though - if Etrata speaks to you or if there is an assassin you particularly want to play with, then go for it.

I'll just note that I love morph, and I'm feeling kind of meh about Etrata in that context. 4 is more than most morphs cost to turn up, and for those that cost more, the discount is 3 max, which is significant, but I don't feel like it will be such a large difference that it becomes a focus. I stopped running Ixidor, Reality Sculptor in Kadena, because the discount ability (3!) came up so infrequently, although I would 100% run Ixidor in Etrata, to get more mileage out of the facedown stuff you steal.

Another issue I see with Etrata in the CZ is that she's pulling in a lot of directions: you want assassins/assassin support, some additional evasion pieces, possibly morph/manifest cards separately, and support for them. Then you need to invest mana to make better use (more than a vanilla 2/2) of whatever you're stealing. There are few assassins that are true threats on their own, whereas many of the horrors are bombs. You get a leg up on Captain in that you can make use of any impactful cards you turn up, whereas horrors are only getting creatures and artifacts.

Both also have some alternate wincons--horrors has mill as a real threat, and Etrata has...Etrata, the Silencer, among other things.

[Cyberium]

There are 69 assassins, and 225 horrors.

Speak of which... isn't Assassin's Creed coming up later this year? O_O I wonder if that'd fill in the gap.