Combat Celebrant + Splinter Twin

Combat Celebrant
Splinter Twin

Requires
All permanents on the battlefield. Splinter Twin attached to Combat Celebrant. Combat Celebrant does not have summoning sickness.
Steps
  1. Activate Combat Celebrant by tapping it, making a token copy of itself with haste
  2. Proceed to your combat step
  3. Declare the Combat Celebrant copy as an attacker, choosing to exert it as it attacks
  4. The Combat Celebrant copy triggers, untapping all other creatures you control and causing you to get an additional combat phase after this one
  5. Repeat
Results
Infinite combat phases. Infinite creature tokens with haste. Infinite ETB. Infinite tap triggers.