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

Skeleton Ship

Intruder Alarm

Geralf's Mindcrusher

Ashnod's Altar

How it works

1. Activate Ashnod's Altar by sacrificing Geralf's Mindcrusher, adding CC.
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 clever loop uses Ashnod's Altar to turn Geralf's Mindcrusher into a reusable sacrifice engine, netting colorless mana while triggering its undying ability to bring it right back. Each time Geralf's Mindcrusher re-enters the battlefield, Intruder Alarm sees the new creature and untaps everything, allowing Skeleton Ship to use its tap ability to place a -1/-1 counter on Geralf's Mindcrusher. Because that -1/-1 counter neatly cancels out the +1/+1 counter from undying, Geralf's Mindcrusher is left completely free to die and trigger the whole cycle over again, milling your opponent out completely in the process.