Agatha's Soul Cauldron + Kiki-Jiki, Mirror Breaker + Cathars' Crusade

Agatha's Soul Cauldron

Kiki-Jiki, Mirror Breaker

Cathars' Crusade

How it works

1. Activate a creature you control with a +1/+1 counter on it using Kiki-Jiki's ability by tapping it, creating a token copy of any nonlegendary creature you control with haste.
2. When the creature token enters the battlefield, Cathars' Crusade triggers, putting a +1/+1 counter on each creature you control.
3. Repeat.

This elegant loop starts by using Agatha's Soul Cauldron to exile Kiki-Jiki, Mirror Breaker, granting its coveted cloning ability to any creature you control that already bears a +1/+1 counter. When you tap that creature to create a token copy of a nonlegendary creature, Cathars' Crusade steps in to reward the new arrival by placing a fresh +1/+1 counter on every creature you control. That newly minted counter ensures your activator is immediately ready to tap for Kiki-Jiki, Mirror Breaker's ability again, generating an unbounded parade of hasty tokens and escalating counters.