Phyrexian Altar + Lingering Tormentor + Hardened Academic

Phyrexian Altar

Lingering Tormentor

Hardened Academic

How it works

1. Activate Phyrexian Altar by sacrificing Lingering Tormentor.
2. When Lingering Tormentor dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Hardened Academic triggers, putting a +1/+1 counter on Lingering Tormentor.
4. Repeat.

This infinite loop is masterminded by the interplay between Lingering Tormentor's persist ability and Hardened Academic's clever triggered ability. When you sacrifice Lingering Tormentor to Phyrexian Altar for a mana, it returns from the graveyard with a -1/-1 counter, but Hardened Academic immediately notices a card leaving the graveyard and places a +1/+1 counter on it; these two counters annihilate each other as a state-based action, leaving the creature completely clean and ready to repeat the cycle indefinitely.