Carrion Feeder, Geralf's Messenger, Intruder Alarm, and Skeleton Ship

Prerequisites

• Carrion Feeder on the battlefield
• Geralf's Messenger on the battlefield
• Intruder Alarm on the battlefield
• Skeleton Ship on the battlefield
• Skeleton Ship does not have summoning sickness
• Geralf's Messenger does not have any +1/+1 counters

Steps

1. Activate Carrion Feeder by sacrificing Geralf's Messenger
2. Geralf's Messenger dies, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it
3. Geralf's Messenger enters the battlefield, triggering itself and Intruder Alarm
4. Resolve the Geralf's Messenger trigger, causing an opponent to lose 2 life
5. Resolve the Intruder Alarm trigger, untapping all creatures
6. Resolve the Carrion Feeder ability from step 1, putting a +1/+1 counter on it
7. Activate Skeleton Ship by tapping it, putting a -1/-1 counter on Geralf's Messenger
8. Repeat

Results

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