Senna, The Redeemer

First strike

When Senna enters or attacks create a
Darkness token with "{t}, Sacrifice this artifact:
Deal 2 damage to target creature or
planeswalker." Your sorceries cast at instant speed.

Level up - When you kill 3 or more units or when
Lucian dies while Senna is under your control, give
her +1/+1 and "Non-creature spells that deal damage
cost {1} less."