Metamorphosis Fanatic, Prowling Geistcatcher, and Ashnod's Altar

Prerequisites

• Metamorphosis Fanatic on the battlefield
• Prowling Geistcatcher on the battlefield
• Ashnod's Altar on the battlefield

Steps

1. Activate Ashnod's Altar by sacrificing Metamorphosis Fanatic
2. When Metamorphosis Fanatic dies, Prowling Geistcatcher's first ability triggers, exiling Metamorphosis Fanatic from your graveyard
3. Activate Ashnod's Altar by sacrificing Prowling Geistcatcher
4. When Prowling Geistcatcher dies, its second ability triggers, returning Metamorphosis Fanatic from exile to the battlefield
5. When Metamorphosis Fanatic enters the battlefield, it triggers, returning Prowling Geistcatcher from your graveyard to the battlefield
6. Repeat

Results

• Infinite LTB
• Infinite ETB
• Infinite sacrifice triggers
• Infinite death triggers
• Infinite colorless mana