Xavier Sal, Infested Captain + Haunted One + Hyrax Tower Scout + Goblin Bombardment

Xavier Sal, Infested Captain

Haunted One

Hyrax Tower Scout

Goblin Bombardment

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 Goblin Bombardment 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 Goblin Bombardment ability, dealing 1 damage to any target.
8. Repeat.

This looping engine relies on untapping Xavier Sal, Infested Captain with Hyrax Tower Scout's entry trigger each time the Scout is sacrificed to Goblin Bombardment. Thanks to Haunted One granting your commander and its tribe undying whenever your commander taps, sacrificing the Scout sends it right back to the battlefield with a +1/+1 counter instead of staying in the graveyard. Xavier Sal's first ability can then strip that counter away to populate your board while tapping to restart the entire sequence, letting you endlessly repeat the loop to deal infinite damage and amass an overwhelming army.