Worth calling out here is the opponent can still sneak/ninjutsu in response if they have another card that can in hand. If you suspect that the opponent plays more than one card with sneak/ninjutsu and has untapped mana, you might want to consider that possibility before targeting the creature.

As an example:

• Opponent declares some creature as an attacker.
• You declare no blockers.
• Opponent casts Michelangelo, returning the attacker to hand, and it resolves.
• You target it with Maze of Ith to remove it from combat. The ability is on the stack, but not yet resolved.
• Opponent casts Donatello, Gadget Master for his sneak cost, returning Michangelo to hand. It resolves.
• Maze of Ith's target is invalid. The ability does nothing.
• Your opponent passes priority, then you pass priority. In the damage step, Donatello deals combat damage to you and triggers.

Basically, during the declare blockers step, sneak/ninjutsu lets you juggle creatures around at instant speed as long as you have the mana.