Omarthis, Ghostfire Initiate + Mirage Mirror + Eldrazi Monument + Mirror Gallery

Omarthis, Ghostfire Initiate

Mirage Mirror

Eldrazi Monument

Mirror Gallery

How it works

1. Put a +1/+1 counter on a colorless creature you control.
2. Omarthis's first triggered ability triggers.
3. In response, activate Mirage Mirror by paying 2, causing it to become a copy of Omarthis until end of turn.
4. Resolve the Omarthis trigger, putting a +1/+1 counter on itself.
5. Mirage Mirror triggers, putting a +1/+1 counter on itself.
6. Omarthis triggers, putting a +1/+1 counter on itself.
7. Repeat from step 5 any number of times.
8. End the loop by declining to place a +1/+1 counter on a creature.
9. 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 elegant loop relies on Mirage Mirror temporarily becoming a copy of Omarthis, Ghostfire Initiate to create a self-sustaining cycle of triggers. Because Mirror Gallery ensures that the legend rule doesn't apply to your multiple Omarthises, each counter placed on one triggers the other to grow in turn, allowing you to generate arbitrarily large creatures. Meanwhile, Eldrazi Monument provides a convenient static anthem that grants your entire team flying and indestructible while you assemble the loop, though you'll want to carefully manage its upkeep sacrifice cost.