Eccentric Apprentice

Flying When this creature enters, venture into the dungeon. (Enter the first room or advance to the next room.) At the beginning of combat on your turn, if you've completed a dungeon, up to one target creature becomes a Bird with base power and toughness 1/1 and flying until end of turn.

From Magic: The Gathering.

Open the interactive version on https://mythscribe.cloud/app/tcg/cards/cms6o8o2z5kh7pb1hgjzjmrq1.