Putrid Imp 
Creature — Zombie Imp
Discard a card: This creature gains flying until end of turn. Threshold — As long as seven or more cards are in your graveyard, this creature gets +1/+1 and can't block.
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyLEGALvintageLEGALcommanderLEGAL