Eccentric Apprentice 

Creature — Tiefling Wizard
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.
Legality
standardNOT LEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL