Fiend Hunter + Carrion Feeder + Metamorphosis Fanatic

Fiend Hunter

Carrion Feeder

Metamorphosis Fanatic

How it works

1. Cast Fiend Hunter by paying its mana cost.
2. When Fiend Hunter enters, its first ability triggers, exiling Metamorphosis Fanatic.
3. Activate Carrion Feeder by sacrificing Fiend Hunter.
4. When Fiend Hunter dies, its second ability triggers, returning Metamorphosis Fanatic from exile to the battlefield.
5. When Metamorphosis Fanatic enters, it triggers, returning Fiend Hunter from your graveyard to the battlefield.
6. When Fiend Hunter enters, its first ability triggers, exiling Metamorphosis Fanatic.
7. Resolve the Carrion Feeder ability.
8. Repeat from step 3.

This clever loop lets you endlessly recycle Fiend Hunter and Metamorphosis Fanatic by leveraging their interlocking enter-the-battlefield and leave-the-battlefield triggers. Each time Fiend Hunter re-enters, it exiles Metamorphosis Fanatic, which in turn immediately brings Fiend Hunter right back from your graveyard whenever Metamorphosis Fanatic is returned to the battlefield. Meanwhile, Carrion Feeder acts as the indispensable sac outlet that makes the loop possible while greedily growing larger with an infinite supply of +1/+1 counters.