Combat Celebrant, and Helm of the Host

Prerequisites

• Combat Celebrant on the battlefield
• Helm of the Host on the battlefield

Steps

1. At the beginning of your combat phase, Helm of the Host triggers, creating a token copy of Combat Celebrant with haste
2. Declare the token Combat Celebrant as an attacker choosing to exert it as it attacks
3. The Combat Celebrant copy triggers, untapping all other creature you control and causing you to get an additional combat phase after this one
4. Repeat

Results

• Infinite combat phases
• Infinite ETB
• Infinite mana creatures you control can produce
• Infinite tapped creature tokens
• Infinite untap of creatures you control