Xavier Sal, Infested Captain + Haunted One + Intruder Alarm + Shilgengar, Sire of Famine

Xavier Sal, Infested Captain

Haunted One

Intruder Alarm

Shilgengar, Sire of Famine

How it works

1. Activate Xavier Sal's first ability by tapping it and removing a +1/+1 counter from the additional nontoken Human, Fungus and/or Pirate if it has one, or any counter from another permanent you control otherwise.
2. Xavier Sal triggers, causing it and all other creatures you control that share a creature type with it to get +2/+0 and gain undying until end of turn.
3. Resolve the Xavier Sal ability, causing you to populate.
4. Activate Shilgengar by sacrificing the additional Human, Fungus and/or Pirate.
5. When the creature dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. When the creature enters the battlefield, Intruder Alarm triggers, untapping all creatures.
7. Resolve the Shilgengar ability
8. Repeat.

This intricate loop hinges on leveraging Xavier Sal, Infested Captain to perpetually generate tokens and fuel your sacrifice engine while Haunted One quietly keeps your creatures cycling through the graveyard with undying. By tapping Xavier Sal, Infested Captain, you trigger Haunted One's passive buff and keyword grant, allowing you to sacrifice that creature to Shilgengar, Sire of Famine to generate a Blood token. Because the sacrificed creature returns immediately with a +1/+1 counter via undying, its return triggers Intruder Alarm to untap all creatures—including Xavier Sal, Infested Captain—readying the board to strip that counter away with Xavier Sal, Infested Captain's first ability to populate and restart the cycle.