This deck runs on an ETB theme, so the creatures mostly have ETB triggers, plus a bunch of cards to flicker them or copy the triggers.  Any instant speed flicker spells will both help you get a few more ETB effects on the stack, but also allow your creatures/permanents to evade targeted removal (unless needed, I would hold such instant spells for protecting creatures).  The core of the deck is 1-2cc creatures that are unblockable, or have shadow (usually unblockable).  They are easy to re-cast, they don't require extra cards to make them unblockable, and they make great targets for auras/equipment/cipher that trigger on attack or combat damage.  Since an unblockable creature will cost 1-2 mana to re-cast, and Satoru's ninjutsu ability costs 4 mana, I would try to focus on putting creatures in the deck that cost 5cc or more... the more they cost, the better value you get, and the better the ETB trigger should be.  But ninjutsu also allows a creature to hit the battlefield without being cast, so it can't be countered by normal counter spells, which makes any creature that might normally be a counter target worthy of ninjutsu.  The Main Deck list above has what I think are the best options to consider, but the Maybeboard has a lot of other options worth looking over too.

Due to the cost of ninjutsu via Satoru I would probably put in at least 10 sources of reusable mana ramp, along with probably about 35 lands.  Most of what you cast is relatively cheap (considering the big creatures will likely be ninjutsu'd in for 4 mana), so I think 35 lands is fair, but to get the engine really running you want to be using ninjutsu once or twice a turn, which will make mana rocks and other ramp sources necessary.  Just remember that any ramp source you choose to put in should hopefully be accessible in the midst of combat (some are triggered to add mana during your first main phase, etc), but the lists I made for you took that into consideration.

Drawing cards is easy in blue (lots of cards that trigger on combat damage to opponents) so I would recommend having about 10 solid draw cards that will each draw a card (or more) for each mana spent to cast that spell.  The faster you get to ninjutsu-in your biggest/baddest creatures, the faster you can try to secure a win, so seeing lots of cards fast will only help.  Unfortunately, some of the best draw cards in blue are not exactly cheap to purchase, so hopefully I found/provided enough other options to get the job done well enough.

There are triggered abilities flying all over the place with these decks, so being able to copy triggers can help a lot.  Satoru's last ability is triggered, so copying it lets you see three more cards and keep another creature, as well as copying any of the ETB triggers you're getting.  While ninjutstu is an activated ability, it doesn't look like copying it will do anything, and there aren't enough other creatures/permanents with activated abilities to justify adding anything to copy those.

To avoid summoning sickness issues, I would plan to re-cast your unblockable creatures during your second main phase, right after you use them with ninjutsu.  This way the same creature can be used for ninjutsu every turn.

It's (kinda) worth noting that when you attack with a creature with first/double strike, then use ninjutsu to swap that creature out for another, the first creature will deal first strike damage during the first strike damage step, then the new creature will deal damage during the second/normal damage step.  There are a few creature options on the Maybeboard list that have haste, first strike, and flying, so they could also be used as targets for ninjutsu instead of an unblockable/shadow creature.

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Fun cards....

Dusk Mangler won't be cast when you ninjutsu it in, so it has no drawback this way.  Great flicker target as well.

Blade of Selves on an unblockable creature = multiple free tokens for ninjutsu targets, assuming you have enough mana and creatures in hand to bring in.  But then you don't have to re-cast your equipped creature, so it's saving you 1+ mana every turn, on top of the creeature token copying shenanigans.  This is a must have in an ETB build, as Blade of Selves can make things crazy on something like Ancient Silver Dragon or Archon of Cruelty, or maybe Astral Dragon...?  But take note that any creature that triggers on attack will not trigger with token copies made by Blade of Selves... they are not declared as attackers, so they don't trigger... so no It That Betrays triggers, sadly.  Also, but a copy of the new print run of Blade of Selves soon, while it's still cheap, because it will go back up in value again in the not-too-distant future.  It's a $15-20 value card, minimum.

Predators' Hour is fun in here!  Lots of unblockable creatures each triggering this = a big pile of exiled cards you can play for the rest of the game, and spend any color to cast... I mean... WOW... for 2cc... and currently less than $1!  (Also, if any creatures you ninjutsu out have first/double strike, it'll trigger twice, once for them, then again with the new creature's damage.)  Predators' Hour allows you to play lands from its exiled cards, so there's a small "ramp" benefit as well, letting you hit more land drops.  In this deck it has tons of value for 2cc.