Cast Karmic Guide by paying {3}{W}{W}.
When Karmic Guide enters the battlefield, it triggers, targeting Metamorphosis Fanatic.
Holding priority, activate Viscera Seer by sacrificing Karmic Guide.
Resolve the Karmic Guide trigger, returning Metamorphosis Fanatic from your graveyard to the battlefield.
When Metamorphosis Fanatic enters the battlefield, it triggers, targeting Karmic Guide.
Holding priority, activate Viscera Seer by sacrificing Metamorphosis Fanatic.
Resolve the Metamorphosis Fanatic trigger, returning Karmic Guide from your graveyard to the battlefield.
Repeat form step 2.

Infinite LTB

Infinite ETB

Infinite sacrifice triggers

Infinite death triggers

Infinite scry 1

Metamorphosis Fanatic

Karmic Guide

Viscera Seer

Activate Viscera Seer by sacrificing Metamorphosis Fanatic.
When Metamorphosis Fanatic dies, Blood Artist triggers, causing you to gain 1 life and target opponent to lose 1 life.
Resolve the Viscera Seer ability.
Activate Viscera Seer by sacrificing Junji.
When Junji dies, it and Blood Artist trigger.
Resolve the Blood Artist trigger, causing you to gain 1 life and target opponent to lose 1 life.
Resolve the Junji trigger, returning Metamorphosis Fanatic from your graveyard to the battlefield and causing you to lose 2 life.
When Metamorphosis Fanatic enters, it triggers, returning Junji from your graveyard to the battlefield.
Resolve the Viscera Seer ability.
Repeat.

Infinite lifeloss

Junji, the Midnight Sky

Blood Artist

Cast Felidar Guardian by paying its mana cost.
When Felidar Guardian enters the battlefield, it triggers, targeting Metamorphosis Fanatic.
Holding priority, activate Altar of Dementia by sacrificing Felidar Guardian.
Resolve the Felidar Guardian ability, blinking Metamorphosis Fanatic.
When Metamorphosis Fanatic enters the battlefield, it triggers, returning Felidar Guardian from your graveyard to the battlefield.
Repeat from step 2.

Infinite mill

Infinite self-mill

Altar of Dementia

Felidar Guardian

Activate Saffi by sacrificing it, targeting Metamorphosis Fanatic
Activate Viscera Seer by sacrificing Metamorphosis Fanatic
When Metamorphosis Fanatic dies, Saffi triggers, returning Metamorphosis Fanatic from your graveyard to the battlefield.
When Metamorphosis Fanatic enters, it triggers, returning Saffi from your graveyard to the battlefield.
Resolve the Viscera Seer ability.
Repeat.

Saffi Eriksdotter

Activate Viscera Seer by sacrificing Metamorphosis Fanatic.
When Metamorphosis Fanatic dies, Prowling Geistcatcher's first ability triggers, exiling Metamorphosis Fanatic from your graveyard.
Resolve the Viscera Seer ability.
Activate Viscera Seer by sacrificing Prowling Geistcatcher.
When Prowling Geistcatcher dies, its second ability triggers, returning Metamorphosis Fanatic from exile to the battlefield.
When Metamorphosis Fanatic enters the battlefield, it triggers, returning Prowling Geistcatcher from your graveyard to the battlefield.
Resolve the Viscera Seer ability.
Repeat.

Prowling Geistcatcher

Cast Metamorphosis Fanatic by paying {4}{B}{B}.
When Metamorphosis Fanatic enters the battlefield, it triggers, targeting Body Double.
Holding priority, activate Altar of Dementia by sacrificing Metamorphosis Fanatic, causing target player to mill cards equal to Metamorphosis Fanatic's power.
Resolve the Metamorphosis Fanatic ability, returning Body Double from your graveyard to the battlefield as a copy of Metamorphosis Fanatic.
When Body Double enters the battlefield, it triggers, targeting Metamorphosis Fanatic.
Holding priority, activate Altar of Dementia by sacrificing Body Double, causing target player to mill cards equal to Body Double's power.
Resolve the Body Double ability, returning Metamorphosis Fanatic from your graveyard to the battlefield.
Repeat from step 2.

Body Double

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 surveil

Perigee Beckoner

Umbral Collar Zealot

Cast Nature's Rhythm from your hand by paying {6}{G}{G} or from your graveyard for its harmonize cost by paying at most {6}{G}{G}{G}{G}, searching your library for Metamorphosis Fanatic and putting it onto the battlefield.
When Metamorphosis Fanatic enters, it and Preston trigger.
Resolve the Metamorphosis Fanatic trigger, returning an applicable target from your graveyard to the battlefield.
Holding priority, activate Altar of Dementia by sacrificing Metamorphosis Fanatic.
Resolve the Preston trigger, creating a token copy of Metamorphosis Fanatic that is a 0/1 Illusion.
When the Metamorphosis Fanatic token enters, it triggers, returning Metamorphosis Fanatic from your graveyard to the battlefield.
Repeat from step 2.

Combos with "Metamorphosis Fanatic"