Aurora Shifter

Creature — Shapeshifter — {1}{U}

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}."