Gojo, Limitless Sorcerer

Ninjutsu {4}{u}{b} ({4}{u}{b}, Return an unblocked attacker you control to hand; Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Gojo, Limitless Sorcerer deals combat damage to a player, look at that player's hand. You may cast a spell from among those cards without paying its mana cost.