Perigee Beckoner, Grimgrin, Corpse-Born, and Metamorphosis Fanatic

Prerequisites

• Perigee Beckoner in hand
• Grimgrin, Corpse-Born on the battlefield
• Metamorphosis Fanatic on the battlefield
• available

Steps

1. Cast Perigee Beckoner for its warp cost by paying
2. When Perigee Beckoner enters, it triggers, targeting Metamorphosis Fanatic
3. Activate Grimgrin by sacrificing Perigee Beckoner
4. Activate Grimgrin by sacrificing Metamorphosis Fanatic
5. When Metamorphosis Fanatic dies, it triggers, returning itself from your graveyard to the battlefield tapped
6. When Metamorphosis Fanatic enters, it triggers, returning Perigee Beckoner from your graveyard to the battlefield
7. When Perigee Beckoner enters, it triggers, targeting Metamorphosis Fanatic
8. Resolve the Grimgrin ability from step 4
9. Repeat from step 3

Results

• Infinite +1/+1 counters on a creature
• Infinite creature ETB
• Infinite creature LTB
• Infinite creature sacrifice triggers
• Infinite death triggers