All-Seeing Arbiter 
Creature — Avatar
Flying Whenever this creature enters or attacks, draw two cards, then discard a card. Whenever you discard a card, target creature an opponent controls gets -X/-0 until your next turn, where X is the number of different mana values among cards in your graveyard.
Legality
standardNOT LEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL