Cast Hollow One either from your hand or from your graveyard by paying at most {1}, causing it to enter the battlefield as a copy of Crosis's Attendant due to Infinite Reflection.
Activate Hollow One by paying {1} and sacrificing it, adding {U}{B}{R}.
If you cast Hollow One from your graveyard, Hollow One is not exiled by Abandoned Sarcophagus due to Infinite Reflection removing Hollow One's cycling ability.
Repeat.

Infinite black mana

Infinite blue mana

Infinite death triggers

Infinite ETB

Infinite LTB

Infinite red mana

Infinite sacrifice triggers

Infinite storm count

Abandoned Sarcophagus

Infinite Reflection

Crosis's Attendant

Hollow One

Cast Sandbar Merfolk either from your hand or from your graveyard by paying {U}, causing it to enter the battlefield as a copy of Crosis's Attendant due to Infinite Reflection.
Activate Sandbar Merfolk by paying {1} and sacrificing it, adding {U}{B}{R}.
If you cast Sandbar Merfolk from your graveyard, Sandbar Merfolk is not exiled by Abandoned Sarcophagus due to Infinite Reflection removing Sandbar Merfolk's cycling ability.
Repeat.

Sandbar Merfolk

Activate Kiki-Jiki by tapping it, creating a token copy of Crosis's Attendant with haste.
Activate the Crosis's Attendant token by paying {1} and sacrificing it, adding {U}{B}{R}.
When the Crosis's Attendant token dies, Kiki-Jiki triggers, untapping itself.
Repeat.

Kiki-Jiki, Mirror Breaker

Thornbite Staff

Activate Kiki-Jiki by tapping it, creating a token copy of Crosis's's Attendant with haste.
Activate the Crosis's Attendant token by paying {1} and sacrificing it, adding {U}{B}{R}.
Activate Pemmin's Aura's first ability by paying {U}, untapping Kiki-Jiki.
Repeat.

Pemmin's Aura

Activate Kiki-Jiki by tapping it, creating a token copy of Crosis's's Attendant with haste.
Activate the Crosis's Attendant token by paying {1} and sacrificing it, adding {U}{B}{R}.
Activate Freed from the Real's second ability by paying {U}, untapping Kiki-Jiki.
Repeat.

Freed from the Real

Activate Orthion's second ability by paying {6}{R}{R}{R} and tapping it, creating five token copies of Crosis's Attendant with haste.
Activate a Crosis's Attendant token by paying {1} and sacrificing it, adding {U}{B}{R}.
When the Crosis's Attendant token dies, Orthion triggers, untapping itself.
Repeat from step 2 for each remaining Crosis's Attendant token.
Repeat from step 1.
Once you have infinite mana, you may forego sacrificing the Crosis's Attendant tokens and/or target any other creature.

Infinite copies of creatures you control with haste

Infinite creature tokens with haste

Orthion, Hero of Lavabrink

Activate Crosis's Attendant by paying {1} and sacrificing it, adding {U}{B}{R}.
When Crosis's Attendant dies, Luminous Broodmoth triggers, returning Crosis's Attendant from your graveyard to the battlefield without a flying counter on it due to Solemnity.
Repeat.

Solemnity

Luminous Broodmoth

Activate Crosis's Attendant by paying {1} and sacrificing it, adding {U}{B}{R}.
Activate Arcbound Reclaimer by removing a +1/+1 counter from it, putting Crosis's Attendant from your graveyard onto the top of your library.
Activate Oracle's Vault's second ability by tapping it, exiling Crosis's Attendant from the top of your library with the ability to play it until end of turn without playing its mana cost.
Cast Crosis's Attendant from exile without paying its mana cost.
Rocco's second ability triggers, putting a +1/+1 counter on Arcbound Reclaimer and creating a Food token.
Activate Clock of Omens by tapping the Food and Crosis's Attendant, untapping Oracle's Vault.
Repeat.

Combos with "Crosis's Attendant"