Ashnod's Altar + Heartmender + Thran Vigil

Ashnod's Altar

Heartmender

Thran Vigil

How it works

1. Activate Ashnod's Altar by sacrificing Heartmender.
2. When Heartmender 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 Heartmender.
4. Repeat.

This clever loop centers around sacrificing Heartmender to Ashnod's Altar to immediately generate a steady stream of colorless mana while sending the creature to the graveyard. Because of persist, Heartmender returns to the battlefield with a -1/-1 counter, but the presence of Thran Vigil cleverly intercepts this drawback by rewarding you with a +1/+1 counter whenever a card leaves your graveyard on your turn. These two opposing counters instantly annihilate each other through state-based actions, leaving Heartmender completely clean and ready to be sacrificed all over again for an endless chain of deaths and mana.