Kaito, Bane of Nightmares

The ninjutsu ability can be activated during the declare blockers step, combat damage step, or end of combat step. If you wait until after the declare blockers step, because all combat damage is dealt at once, Kaito won't normally deal combat damage.

Kaito enters attacking the same player, planeswalker, or battle the returned creature was attacking. This is a rule specific to ninjutsu; in other cases, when a creature is put onto the battlefield attacking, that creature's controller chooses which player, planeswalker, or battle it's attacking.

If at least one creature in combat has first strike or double strike, you can activate Kaito's ninjutsu ability during the first-strike combat damage step. In that case, Kaito will deal combat damage during the regular combat damage step, even if he has first strike.