Phyrexian Altar + Thran Vigil

Phyrexian Altar

Thran Vigil

How it works

1. Activate Phyrexian Altar by sacrificing the creature with persist.
2. When that creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Thran Vigil triggers, putting a +1/+1 counter on that creature.
4. Remove a +1/+1 counter and a -1/-1 counter from that creature as a state-based action.
5. Repeat.