Moritte of the Frost + Omarthis, Ghostfire Initiate + Mirror Box

Moritte of the Frost

Omarthis, Ghostfire Initiate

Mirror Box

How it works

1. Cast Moritte of the Frost by paying 2 plus commander tax (if applicable).
2. Choose to have Moritte of the Frost enter the battlefield as a copy of Omarthis with two +1/+1 counters on it.
3. Omarthis's first triggered ability triggers, putting a +1/+1 counter on itself.
4. Moritte of the Frost triggers, putting a +1/+1 counter on itself.
5. Repeat from step 3 any number of times.
6. End the loop by declining to put a +1/+1 counter on one of your creatures.
7. Warning: Omarthis's last ability can increase the risk of losing by drawing from an empty library if you place enough counters on them.

This clever loop hinges on turning Moritte of the Frost into a copy of Omarthis, Ghostfire Initiate, letting you bypass the usual legendary restrictions thanks to Mirror Box. Because the resulting copy is both a creature and colorless, every time a counter is placed on one of these entities, Omarthis's ability triggers to fuel the other, creating a self-sustaining loop that piles infinite +1/+1 counters onto your board. You can repeat this process as many times as you like, though you'll want to watch out for Omarthis's death trigger later so you don't accidentally manifest your entire library into the graveyard!