Combat Celebrant | Unforgiving One | Mirror Image

(and two other cards)

Declare
Combat Celebrant and
Unforgiving One as attackers, choosing to exert
Combat Celebrant as it attacks.
Combat Celebrant triggers, untapping all other creatures you control and causing you to get an additional combat phase after this one.
Unforgiving One triggers, returning
Mirror Image from your graveyard to the battlefield as a copy of
Combat Celebrant.
Activate
Altar of Dementia by sacrificing
Combat Celebrant, causing target player to mill cards equal to
Combat Celebrant's power.
Move to your next combat phase.
Declare
Mirror Image and
Unforgiving One as attackers, choosing to exert
Mirror Image as it attacks.
Mirror Image triggers, untapping all other creatures you control and causing you to get an additional combat phase after this one.
Unforgiving One triggers, returning
Combat Celebrant from your graveyard to the battlefield.
Activate
Altar of Dementia by sacrificing
Mirror Image, causing target player to mill cards equal to
Mirror Image's power.
Repeat.