Phyrexian Altar + Resourceful Defense

Phyrexian Altar

Resourceful Defense

How it works

1. Activate Phyrexian Altar by sacrificing the persist creature that has a +1/+1 counter on it, adding one mana of any color.
2. When that creature dies, its persist ability and Resourceful Defense trigger.
3. Resolve Resourceful Defense's ability, putting at least two +1/+1 counters onto the surviving persist creature due to the counter-increasing effect.
4. If that creature had a -1/-1 counter on it, remove that and one of the +1/+1 counters from it as a state-based action.
5. Resolve the persist ability from step 2, returning the persist creature from your graveyard to the battlefield with a -1/-1 counter.
6. Repeat.