A more streamlined UB version of a Ninjas deck that I brewed previously Ninjas! that is based more off of a list Corbin Hosler played and that 5-0'd a league (video here), but also drawing some inspiration from a decklist by Gariel Nassif. Frank Lepore also had a Ninjas list a while ago and Ninjas (albeit a very different list) have appeared in Vintage too.
The main premise of the deck is to sneak in ninjas, like Ingenious Infiltrator, and generate lots of card advantage. To help get your ninjas into play, there are a bunch of evasive creatures, like Changling Outcast, Vendilion Clique, and Spellstutter Sprite that all have great ETB abilities. Faerie Seer is another evasive 1-drop that helps smooth out your draws to help you hit lands (which Corbin did seem to get manascrewed a couple times).
Main Deck
Compared to the other list I mentioned above, this deck cuts Green entirely, so no Birds, Ice-Fang Coalt|Coatl, or Abrupt Decay and no Assassin's Trophy and Veil of Summer/Collector Ouphe in the board. I took out all the Spectral Sailors, a Mist-Syndicate Naga, Brazen Borrower, and Tyrant's Scorn compared to the list Corbin was playing because I wanted to have more room for countermagic and removal (mostly just a playstyle preference).
Creatures
I want to draw special attention though to Changling Outcast - this card really pulls its weight. It can't be blocked, meaning you can rely on it to get a ninja into play. It's a fairy for Spellstutter Sprite, a wizard for Wizard's Retort, and, most importantly, a ninja for Infiltrator, allowing you to get a steady stream of card advantage.
Rounding out the rest of the creatures, we have Snapcaster Mage (yet another ETB effect, although having an unblocked Snapcaster will be difficult for Ninjuitsuing back), and Fallen Shinobi at the top end.
Non-Creature Spells
For non-creature spells, there's countermagic and removal. I'm not playing any Cryptics or Charms as those have very strict mana requirements and we're going to be playing spells or sneaking in ninjas on our turn, so we won't have lots of mana at our disposal on our opponents turn. So instead, I chose to include Force, Spell Pierce, and Wizard's Retort. They're all very cheap, flexible answers to our opponent's spells, although I'm not sure if I should have mainboard Spell Pierce as Force fills the same role. It may be correct to remove Pierce in favor of Force and/or Retort/Drown. I chose Wizard's Retort because we have 16 wizards in our deck (Changling Outcast, Spellstutter Sprite, Vendilion Clique, Faerie Seer, and Snapcaster) - that should be enough to make it Counterspell consistently. Given we're only two colors, the UU cost of it isn't that much of a downside and it's just a strictly better Mana Leak. I also toyed with the idea of using Familiar's Ruse so we can get back a creature with an ETB ability (like decks that are using Deprive to buyback Mystic Sanctuary), but I decided that overall it'd probably be better to keep a board presence and opted for Retort (although I'm definitely curious to try out Ruse). We also have Fatal Push and Dismember as they're the best cheap creature removal and Drown in the Loch as creature removal and another counter spell.
Manabase
I'm always kinda guessing with the manabase, any suggestions are welcome! I more or less copied what Corbin was playing, but I added in Vistas so as to have more fetches for thinning the deck (we REALLY don't want to flood!). I also don't really like Castle Vantress - if we're ever tapping 5 mana to Scry 2, then that's really not a good sign. I could see changing that to another basic, Watery Grave, or Drowned Catacomb.
Other thoughts
I don't have Brazen Borrower in the main although I probably should. I our opponent ever resolves a non-creature spell, we don't have any way of dealing with it. So even though Petty Theft isn't that great of an answer, it is something to combat Blood Moon, Teferi, and possibly Chalice of the Void.
Sideboard
Pretty typical sideboard for today's meta: Ashiok and Nihil Spellbomb for Uro, Dredge, Kroxa and other graveyard decks; Ashiok and Damping Sphere for Titan, and Tron; Ashiok, Sphere, Collective Brutality, and Thoughtseize for combo decks; Brutality, Sphere, and another Drown in the Loch for red decks, Wizard's Retort for more countermagic; and Brazen Borrower if we ever need to bounce non-creature permanents. I could see cutting Brutality and a Spellbomb for other cards that'll help in more difficult matchups, happy to hear other suggestions too!
Closing Remarks
That's about all I have to say about this deck. I'd very much like to hear the community's thoughts and get whatever constructive comments I can!
