Combat Celebrant and Mirage Phalanx on the battlefield.
Mirage Phalanx is paired with Combat Celebrant.
Steps
At the beginning of combat on your turn, Mirage Phalanx and Combat Celebrant each trigger.
Resolve the Mirage Phalanx trigger, creating a token copy of it with haste and without soulbond.
The Mirage Phalanx token enters the battlefield, triggering Mirage Phalanx's soulbond ability.
Resolve the Mirage Phalanx trigger, choosing not to pair it with the Mirage Phalanx token.
Resolve the Combat Celebrant trigger from step 1, creating a token copy of it with haste.
The Combat Celebrant token enters the battlefield, triggering Mirage Phalanx's soulbond ability.
Resolve the Mirage Phalanx trigger, choosing not to pair it with the Combat Celebrant token.
Declare the Combat Celebrant token as an attacker.
The Combat Celebrant token triggers, allowing you to exert it to untap all other creatures you control and get an additional combat phase after this one.