U/B Ninja control deck. Yuriko, the Tiger's ShadowGC and Ingenious Infiltrator are Ninja of the Deep Hours that also make your Thousand-Faced Shadow and Changeling Outcast ninja enablers into card draw. I decided to go light on removal for a couple reasons. Partially it's the combo nature of Legacy; not everybody will be on unfair decks, but the unfair decks are powerful and fast. Partially it's an old propensity to side some maindeckable staples to just bring in whenever some of my cards are bad. I also think this deck can race fair decks fairly easily. While the 1 drops are pretty mediocre, our 2 drop slot is stacked.
Baleful Strix makes your ninjas into a self bounce engine, and also are evasive for the ninjas. Deathtouch means they trade above their weight class, which could be important. Dauthi Voidwalker is another evasive threat, as well as maindeck grave hate, relevant in a format with Reanimate.
Force of WillGC, Daze, and Thoughtseize gives us some solid interaction that should generally be live. Fatal Push and Dismember give us answers for the fair midrange and tempo deck, with a couple backup Pushes in the sideboard for fair matches. Due to the nature of ninjutsu, push has even more ways to address 3 and 4 drops.
The mana base is simply stolen. It makes sense to only run 2 Wasteland, between Dauthi Voidwalker needing BB and so many of our cards needing UB. One more is in the side for matchups where attacking lands or boarding in an additional land. The only change I made to the mana base was to split the blue fetches, because of Pithing Needle.
It's a Brainstorm deck, but due to the ability to draw multiple cards in a turn it clears off the topdeck fairly easily, meaning it's less reliant than some decks on fetches to make Brainstorm good. Simply stacking a FOW before you hit with Yuriko is already really good, and the deck needs the consistency of Brainstorm to avoid hands that have too many Thousand-Faced Shadow or Changeling Outcast which are cards that are good to see, even in multiples, provided you see your ninjutsu monsters. Honestly, if you don't ever see Yuriko or Infiltrator, you're probably losing the game anyways, so digging 3 cards deeper and shuffling excess chaff and lands feels absolutely essential. I ultimately decided no to include Kaito, because the deck already runs seven ninjutsu 2 targets, and Thousand-Faced Shadow being both an enabler for Ninjutsu and a payoff for having an unblocked creature - a 3 mana planeswalker, even a planeswalker that attacks, is too slow.
You could run Ponder. Card is nuts. The thing to cut would be Thoughtseize. However, thoughtseize is both good against the unfair decks that we don't have any chance to race, and good at giving us information in control mirrors, which is invaluable, and the card isn't bad against fair decks. It's pretty much the only interactive spell in the deck that will be good no matter the matchup, and it makes sense to target combo and control over removal for Delver, where we're basically both playing a fair creature game, and my creatures snowball. Of course, Thoughtseize is also particularly worse going second than first, but that's true of virtually every card not named Force of Will.
I considered Chain of Vapor in the sideboard to give me a flexible removal option against Reanimator as well as Artifacts and Enchantments, but given the main thing you're siding removal in to deal with is Orcish BowmastersGC Fatal Push, while not perfect, is a lot better in that scenario.
