Skeleton Ship + Intruder Alarm + Geralf's Mindcrusher + Phyrexian Altar

Skeleton Ship

Intruder Alarm

Geralf's Mindcrusher

Phyrexian Altar

How it works

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

This loop hinges on constantly recycling Geralf's Mindcrusher using Phyrexian Altar to feed it to the graveyard, where its undying ability brings it right back with a +1/+1 counter. Because Intruder Alarm untaps all creatures whenever anything enters the battlefield, you can tap Skeleton Ship to place a -1/-1 counter on Geralf's Mindcrusher, neutralizing the counter it returned with so undying can trigger again on the next sacrifice. This elegant exchange lets you mill your opponent out while generating an infinite supply of colored mana and death triggers.