Infinite creature ETBInfinite creature LTBInfinite combat phasesInfinite creature tokens with hasteInfinite death triggersInfinite mana creatures you control can produceInfinite creature sacrifice triggersInfinite untap of creatures you control
How it works
Declare Grub and Combat Celebrant as attackers, choosing to exert Combat Celebrant as it attacks. Grub and Combat Celebrant trigger.
Resolve the Grub trigger, putting a -1/-1 counter on Combat Celebrant and then creating a tapped and attacking token copy of it.
Combat Celebrant dies as a state-based action due to having 0 toughness.
Resolve the Combat Celebrant trigger, causing you to untap all other creatures you control and causing you to get an additional combat phase after this one.
Repeat each combat phase, using the Combat Celebrant token instead.
This brilliant recursive engine leverages Grub, Storied Matriarch // Grub, Notorious Auntie to repeatedly clone and sacrifice a lethal combat threat. By using Grub's attack trigger to blight Combat Celebrant—putting a -1/-1 counter on it that immediately sends it to the graveyard as a state-based action—you generate a fresh token copy of Combat Celebrant that enters the battlefield ready to attack. Urabrask the Hidden ensures that this newly spawned token enters the fray immediately with haste, allowing you to chain infinite combat phases and endless creature tokens through the combined prowess of Combat Celebrant's exertion and Grub's transformation loop.