Satoru Umezawa

Once you activate a ninjutsu ability, no player can affect that ability by removing Satoru Umezawa from the battlefield. Even if Satoru leaves the battlefield before it resolves, you'll still be able to put the creature onto the battlefield tapped and attacking.

The ninjutsu ability can be activated during the declare blockers step, combat damage step, or end of combat step. In most cases (see below), if you wait until the combatdamage step or end of combat step, it will be after combat damage has been dealt, so the Ninja won't deal combat damage.

As you activate a ninjutsu ability, you reveal the Ninja card in your hand and return the attacking creature. The Ninja card stays revealed and isn't put onto the battlefield until the ability resolves. If it leaves your hand before then, it won't enter the battlefield at all.

Puff of smoke not included.

Satoru Umezawa's triggered ability triggers whenever you activate a ninjustsu ability, and it will resolve before that ability resolves. The card with ninjustsu will still be in your hand while resolving the ability and must remain revealed until the ninjutsu ability resolves or is otherwise removed from the stack.