Geralf's Messenger, Intruder Alarm, Phyrexian Altar, and Skeleton Ship

Prerequisites

• Geralf's Messenger on the battlefield
• Intruder Alarm on the battlefield
• Phyrexian Altar 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 Phyrexian Altar by sacrificing Geralf's Messenger, adding one mana of any color
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. Activate Skeleton Ship by tapping it, putting a -1/-1 counter on Geralf's Messenger
7. Repeat

Results

• Infinite colored mana
• Infinite death triggers
• Infinite ETB
• Infinite lifeloss
• Infinite LTB
• Infinite sacrifice triggers
• Infinite untap of all creatures