How can you create a combo with Combat Celebrant, Unforgiving One, Clone, Altar of Dementia, Mass Hysteria?
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[START OF COMBO]This combo can be formed with Combat Celebrant, Unforgiving One, Clone, Altar of Dementia, Mass Hysteria

Color identity: UBR
Mana cost: 
Steps:
  1. Declare Combat Celebrant and Unforgiving One as attackers, choosing to exert Combat Celebrant as it attacks.
  2. Combat Celebrant triggers, untapping all other creatures you control and causing you to get an additional combat phase after this one.
  3. Unforgiving One triggers, returning Clone from your graveyard to the battlefield as a copy of Combat Celebrant.
  4. Activate Altar of Dementia by sacrificing Combat Celebrant, causing target player to mill cards equal to Combat Celebrant's power.
  5. Move to your next combat phase.
  6. Declare Clone and Unforgiving One as attackers, choosing to exert Clone as it attacks.
  7. Clone triggers, untapping all other creatures you control and causing you to get an additional combat phase after this one.
  8. Unforgiving One triggers, returning Combat Celebrant from your graveyard to the battlefield.
  9. Activate Altar of Dementia by sacrificing Clone, causing target player to mill cards equal to Clone's power.
  10. Repeat.[END OF COMBO STEPS]

Result:
  - Infinite combat phases
  - Infinite mana creatures you control can produce
  - Infinite mill
  - Infinite self-mill
  - Infinite untap of creatures you control[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - Combat Celebrant must be on the battlefield
  - Unforgiving One must be on the battlefield
  - Clone must be in the graveyard
  - Altar of Dementia must be on the battlefield
  - Mass Hysteria must be on the battlefield
  - You control at least five modified creatures.
  - An opponent is unable to block and kill creatures you control.
  - You control a Mountain.
[END OF COMBO PREREQUISITES]
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