Aurora Shifter is a rare Creature — Shapeshifter card from Modern Horizons 3 Commander (M3C), collector number 45. Current market price: $0.98, TCGplayer market prices via Scryfall.
Whenever this creature deals combat damage to a player, you get that many {E}. At the beginning of combat on your turn, you may pay {E}{E}. When you do, this creature becomes a copy of another target creature you control, except it has this ability and "Whenever this creature deals combat damage to a player, you get that many {E}."