Xavier Sal, Infested Captain + Haunted One + Hyrax Tower Scout + Shilgengar, Sire of Famine

Xavier Sal, Infested Captain

Haunted One

Hyrax Tower Scout

Shilgengar, Sire of Famine

How it works

1. Activate Xavier Sal's first ability by tapping it and removing a +1/+1 counter from Hyrax Tower Scout 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 Hyrax Tower Scout.
5. When Hyrax Tower Scout dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. When Hyrax Tower Scout enters the battlefield, it triggers, untapping Xavier Sal.
7. Resolve the Shilgengar ability
8. Repeat.

This intricate loop relies on Xavier Sal, Infested Captain operating as the engine, using its tap ability to populate while quietly leveraging Haunted One to grant your team undying the moment Xavier Sal taps. Shilgengar, Sire of Famine acts as the sacrificial outlet, feeding on creatures to generate Blood tokens while sending them to the graveyard. When Hyrax Tower Scout is sacrificed, undying brings it straight back to the battlefield with a +1/+1 counter, whose entry trigger immediately untaps Xavier Sal so the process can begin anew.