Xavier Sal, Infested Captain + Haunted One + Hyrax Tower Scout + Carrion Feeder

Xavier Sal, Infested Captain

Haunted One

Hyrax Tower Scout

Carrion Feeder

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 Carrion Feeder 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 Carrion Feeder ability, putting a +1/+1 counter on it.
8. Repeat.

This clever loop hinges on Haunted One granting your commander the ability to hand out undying whenever it taps, turning your graveyard into a revolving door for your creatures. You begin by tapping Xavier Sal, Infested Captain to populate, which triggers Haunted One and sets up the sacrifice chain. By feeding Hyrax Tower Scout to Carrion Feeder, you trigger the Scout's undying return—fueled by Haunted One's static bestowal of the keyword—and its entrance untaps Xavier Sal, Infested Captain to do it all over again.