Impostor Syndrome + Combat Celebrant + Tannuk, Steadfast Second

Impostor Syndrome

Combat Celebrant

Tannuk, Steadfast Second

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 revolves around Combat Celebrant's ability to grant extra combat phases by exerting itself, which normally leaves you stuck with an exhausted creature. Impostor Syndrome solves this neatly by minting nonlegendary token copies whenever your creatures deal combat damage, supplying a fresh, un-exerted Combat Celebrant for the next assault. Meanwhile, Tannuk, Steadfast Second ensures your newly minted token copies can charge right back into battle immediately by giving all your other creatures haste.