Evolution Witness + Tarrian's Soulcleaver + Dark Sphere

Evolution Witness

Tarrian's Soulcleaver

Dark Sphere

How it works

1. Cast Dark Sphere by paying 0.
2. Activate Dark Sphere by tapping and sacrificing it.
3. Tarrian's Soulcleaver triggers, putting a +1/+1 counter on Evolution Witness.
4. Evolution Witness triggers, returning Dark Sphere from your graveyard to your hand.
5. Resolve the Dark Sphere ability.
6. Repeat.