Impostor Syndrome + Combat Celebrant + Urabrask the Hidden

Prerequisites

• An opponent cannot block creatures you control.
• Combat Celebrant has vigilance.

Steps

1. 1Declare 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. 2Deal combat damage to an opponent using Combat Celebrant, triggering Impostor Syndrome, creating a token copy of Combat Celebrant that isn't legendary.
3. 3During 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. 4The Combat Celebrant token triggers, causing you to untap all other creatures you control and to get an additional combat phase after this one.
5. 5Repeat from step 2.

Effects

• Infinite combat damage
• Infinite combat phases
• Infinite creature ETB
• Infinite creature LTB
• Infinite creature sacrifice triggers
• Infinite death triggers
• Infinite mana creatures you control can produce
• Infinite untap of creatures you control