Xavier Sal, Infested Captain + Haunted One + Hyrax Tower Scout + Umbral Collar Zealot

Xavier Sal, Infested Captain

Haunted One

Hyrax Tower Scout

Umbral Collar Zealot

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 Umbral Collar Zealot 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 Umbral Collar Zealot ability, putting a +1/+1 counter on it.
8. Repeat.

This ingenious engine turns your commander into a one-man army by looping Hyrax Tower Scout through the graveyard and back again. The key passive enabler is Haunted One, which grants your commander and its tribe undying whenever they become tapped—allowing Xavier Sal, Infested Captain to give the Scout a new lease on life every time he taps to populate. Meanwhile, Umbral Collar Zealot provides the necessary sacrifice outlet to trigger that undying return, setting up a continuous cycle where the newly reanimated Hyrax Tower Scout enters the battlefield, untaps Xavier Sal, and lets you repeat the process indefinitely for boundless value and infinite triggers.