Xavier Sal, Infested Captain + Animation Module + Intruder Alarm

Xavier Sal, Infested Captain

Animation Module

Intruder Alarm

How it works

1. Activate a mana-producing creature by tapping it, adding at least 1.
2. Activate Xavier Sal's second ability by tapping it and sacrificing another creature, causing you to put a +1/+1 counter on a creature you control.
3. Animation Module triggers, causing you to pay 1 to create a 1/1 Servo artifact creature token.
4. When the Servo enters the battlefield, Intruder Alarm triggers, untapping all creatures.
5. Repeat.
6. Once you have infinite +1/+1 counters on a creature, you may instead use Xavier Sal's first ability to get infinite copies of creature tokens you control.

This loop turns a simple sacrifice into a perpetual motion machine by leveraging Intruder Alarm to untap your entire board every time a new creature arrives. As Xavier Sal, Infested Captain sacrifices a creature to proliferate, it feeds Animation Module's trigger, which asks for just one mana to churn out a fresh Servo artifact creature token. That token's entry immediately fires off Intruder Alarm's static untap ability, returning your mana producers and Xavier Sal to a ready state so you can repeat the process indefinitely. Once you've scaled this engine to build towering +1/+1 counters, you can pivot Xavier Sal's first ability to repeatedly populate your battlefield with infinite copies of your favorite creature tokens.