Phyrexian Altar + Yuna, Grand Summoner

Phyrexian Altar

Yuna, Grand Summoner

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 Yuna trigger.
3. Resolve Yuna'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.