Thermopod + Fiend Hunter + Metamorphosis Fanatic

Thermopod

Fiend Hunter

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 Thermopod 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. Repeat from step 3.