Skeleton Ship + Intruder Alarm + Flayer of the Hatebound + Phyrexian Altar

Skeleton Ship

Intruder Alarm

Flayer of the Hatebound

Phyrexian Altar

How it works

1. Activate Phyrexian Altar by sacrificing Flayer of the Hatebound, adding one mana of any color.
2. Flayer of the Hatebound dies, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
3. Flayer of the Hatebound enters the battlefield, triggering itself and Intruder Alarm.
4. Resolve the Flayer of the Hatebound trigger, dealing damage equal to its power to any target.
5. Resolve the Intruder Alarm trigger, untapping all creatures.
6. Activate Skeleton Ship by tapping it, putting a -1/-1 counter on Flayer of the Hatebound.
7. Repeat.

This clever setup turns a ghostly vessel into a devastating engine by combining mana production with creature recursion. You begin by using Phyrexian Altar to sacrifice Flayer of the Hatebound for mana, which triggers its undying ability to return it to the battlefield with a +1/+1 counter and fires off its damage ability. Every time the Flayer re-enters from the graveyard, Intruder Alarm untaps all creatures, including Skeleton Ship. You then use Skeleton Ship to place a -1/-1 counter on Flayer of the Hatebound, which immediately neutralizes its +1/+1 counter through state-based actions so it can safely die and repeat the loop again.