Mikaeus, the Unhallowed, Bloodied Ghost, and Hammerhead, Maggia Boss

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Bloodied Ghost on the battlefield
• Hammerhead, Maggia Boss on the battlefield

Steps

1. Activate Hammerhead by sacrifiicing Bloodied Ghost
2. When Bloodied Ghost dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it
3. When it enters, Bloodied Ghost will put a -1/-1 counter on itself, removing the +1/+1 counter
4. Resolve the Hammerhead ability
5. Repeat
6. Activate Hammerhead by sacrificing Bloodied Ghost
7. When Bloodied Ghost dies, its undying ability triggers, returning it from your graveyard to the battlefield without a +1/+1 counter on it due to its replacement effect
8. Resolve the Hammerhead ability Repeat

Results

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