Nim Deathmantle, Ashnod's Altar, and Garrison Cat

Prerequisites

• Nim Deathmantle on the battlefield
• Ashnod's Altar on the battlefield
• Garrison Cat on the battlefield

Steps

1. Activate Ashnod's Altar by sacrificing Garrison Cat, adding
2. When Garrison Cat dies, it and Nim Deathmantle trigger, Resolve the Garrison Cat trigger, creating a creature token
3. Holding priority, activate Ashnod's Altar by sacrificing a creature token, adding
4. Resolve the Nim Deathmantle trigger, causing you to pay to return Garrison Cat from your graveyard to the battlefield and attach Nim Deathmantle to it
5. Repeat

Results

• Infinite creature ETB
• Infinite creature LTB
• Infinite creature sacrifice triggers
• Infinite death triggers