Cast Perigee Beckoner for its warp cost by paying {1}{B}.
When Perigee Beckoner enters, it triggers, targeting Metamorphosis Fanatic.
Activate Umbral Collar Zealot by sacrificing Perigee Beckoner.
Activate Umbral Collar Zealot by sacrificing Metamorphosis Fanatic.
When Metamorphosis Fanatic dies, it triggers, returning itself from your graveyard to the battlefield tapped.
When Metamorphosis Fanatic enters, it triggers, returning Perigee Beckoner from your graveyard to the battlefield.
When Perigee Beckoner enters, it triggers, targeting Metamorphosis Fanatic.
Resolve the Umbral Collar Zealot ability from step 4.
Repeat from step 3.

Infinite LTB

Infinite ETB

Infinite sacrifice triggers

Infinite death triggers

Infinite surveil

Perigee Beckoner

Umbral Collar Zealot

Metamorphosis Fanatic

Cast Illicit Masquerade by paying {3}{B}. When it enters, its first ability triggers, putting an impostor counter on Skullbriar.
Cast Perigee Beckoner for its warp cost by paying {1}{B}.
When Perigee Beckoner enters, it triggers, targeting Skullbriar.
Activate Carrion Feeder by sacrificing Perigee Beckoner.
Activate Carrion Feeder by sacrificing Skullbriar.
When Skullbriar dies, Illicit Masquerade's second ability and Skullbriar's ability granted to it by Perigee Beckoner trigger.
Resolve the Skullbriar trigger, returning it from your graveyard to the battlefield.
Resolve the Illicit Masquerade trigger, failing to exile Skullbriar as it has left your graveyard and returning Perigee Beckoner from your graveyard to the battlefield.
Resolve the Carrion Feeder ability from step 5.
Repeat from step 3.

Infinite +1/+1 counters on a creature

Skullbriar, the Walking Grave

Illicit Masquerade

Carrion Feeder

Cast Perigee Beckoner for its warp cost by paying {1}{B}.
When Perigee Beckoner enters, it triggers, targeting Ruthless Technomancer.
Activate Nim Shambler by sacrificing Ruthless Technomancer.
When Ruthless Technomancer dies, its ability given to it by Perigee Beckoner triggers, returning Ruthless Technomancer from your graveyard to the battlefield tapped.
When Ruthless Technomancer enters, its first ability triggers, causing you to sacrifice Nim Shambler and creating a number of Treasure tokens equal to Nim Shambler's power.
Resolve the Nim Shambler ability from step 3.
Activate six Treasures by tapping and sacrificing them, adding {4}{B}{B}.
Activate Ruthless Technomancer by paying {2}{B} and sacrificing two Treasures, returning Nim Shambler from your graveyard to the battlefield.
Activate Nim Shambler by sacrificing Perigee Beckoner.
Activate Ruthless Technomancer by paying {2}{B} and sacrificing four Treasures, returning Perigee Beckoner from your graveyard to the battlefield.
Repeat from step 2.

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