Gravespawn Sovereign, Intruder Alarm, and Carrion Feeder

Prerequisites

• Gravespawn Sovereign on the battlefield
• Intruder Alarm on the battlefield
• Carrion Feeder on the battlefield
• You control at least three other Zombies and an additional nontoken creature

Steps

1. Activate Carrion Feeder by sacrificing a nontoken creature, putting a +1/+1 counter on it
2. Activate Gravespawn Sovereign by tapping five untapped Zombies you control, returning any creature from your graveyard to the battlefield
3. The creature enters the battlefield, triggering Intruder Alarm, untapping all creatures
4. Repeat

Results

• Infinite +1/+1 counters on Carrion Feeder
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite sacrifice triggers
• Infinite untap of creatures