Kaseto, Orochi Archmage

Oracle Text

GU: Target creature can't be blocked this turn. If that creature is a Snake, it gets +2/+2 until end of turn.

Card Rulings

11/4/2015 Once a creature has been legally blocked, activating Kaseto’s ability targeting that creature won’t cause it to become unblocked. It will give it +2/+2 if it’s a Snake, though.