Ashnod's Altar + Twilight Shepherd + Thran Vigil

Ashnod's Altar

Twilight Shepherd

Thran Vigil

How it works

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

This ingenious loop turns Twilight Shepherd into a self-sustaining mana engine with the help of Ashnod's Altar to sacrifice the angel for two colorless mana. Every time Twilight Shepherd dies, its persist ability brings it back to the battlefield bearing a -1/-1 counter, but Thran Vigil steps in during your turn to counteract this drawback by placing a +1/+1 counter on it whenever it leaves the graveyard, effectively neutralizing the counters and allowing the cycle to repeat indefinitely.