Skeleton Ship + Intruder Alarm + Geralf's Mindcrusher + Altar of Dementia

Skeleton Ship

Intruder Alarm

Geralf's Mindcrusher

Altar of Dementia

How it works

1. Activate Altar of Dementia by sacrificing Geralf's Mindcrusher.
2. Geralf's Mindcrusher dies, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
3. Geralf's Mindcrusher enters the battlefield, triggering itself and Intruder Alarm.
4. Resolve the Geralf's Mindcrusher trigger, causing target player to mill five cards.
5. Resolve the Intruder Alarm trigger, untapping all creatures.
6. Resolve the Altar of Dementia ability from step 1, causing target player to mill cards equal to Geralf's Mindcrusher's power.
7. Activate Skeleton Ship by tapping it, putting a -1/-1 counter on Geralf's Mindcrusher.
8. Repeat.

This cunning loop uses Altar of Dementia to sacrifice Geralf's Mindcrusher, milling your opponent while triggering its undying ability to bring it right back to the battlefield with a +1/+1 counter. Every time Geralf's Mindcrusher re-enters, Intruder Alarm triggers to untap your entire board, which cleverly lets you tap Skeleton Ship to place a -1/-1 counter on Geralf's Mindcrusher—instantly neutralizing the +1/+1 counter so the undying cycle can happen all over again. By repeating this process, you mill your opponent's entire library while generating an infinite storm of creature deaths, entries, and untaps.