Impostor Syndrome + Combat Celebrant + Fires of Yavimaya

Impostor Syndrome

Combat Celebrant

Fires of Yavimaya

How it works

1. Declare Combat Celebrant as an attacker, choosing to exert it as it attacks and triggering its ability, causing you to untap all other creatures you control and to get an additional combat phase after this one.
2. Deal combat damage to an opponent using Combat Celebrant, triggering Impostor Syndrome, creating a token copy of Combat Celebrant that isn't legendary.
3. During your next combat phase, declare Combat Celebrant and the Combat Celebrant token as attackers, choosing to exert the Combat Celebrant token as it attacks.
4. The Combat Celebrant token triggers, causing you to untap all other creatures you control and to get an additional combat phase after this one.
5. Repeat from step 2.

This loop transforms a single extra combat phase into an endless march by turning your attackers into a self-replicating army. Thanks to Fires of Yavimaya granting haste, every new copy you create can jump straight into the fray immediately. When you attack with Combat Celebrant and successfully deal combat damage, Impostor Syndrome steps in to clone it, leaving you with a fresh nonlegendary token ready to be exerted in the next combat phase. Because that token can also be exerted to untap your creatures and grant yet another combat step, you can repeat this vicious cycle forever to generate infinite combat phases and damage.