Activate Saffi by sacrificing it, targeting Extraction Specialist.
Activate Altar of Dementia by sacrificing Extraction Specialist.
When Extraction Specialist dies, Saffi triggers, returning Extraction Specialist from your graveyard to the battlefield.
When Extraction Specialist enters the battlefield, it triggers, returning Saffi from your graveyard to the battlefield.
Resolve the Altar of Dementia ability from step 2, causing target player to mill cards equal to Extraction Specialist's power.
Repeat.

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite mill

Infinite creature sacrifice triggers

Infinite self-mill

Saffi Eriksdotter

Extraction Specialist

Altar of Dementia

Activate Saffi by sacrificing it, targeting Extraction Specialist.
Activate Ashnod's Altar by sacrificing Extraction Specialist, adding {C}{C}.
When Extraction Specialist dies, Saffi triggers, returning Extraction Specialist from your graveyard to the battlefield.
When Extraction Specialist enters the battlefield, it triggers, returning Saffi from your graveyard to the battlefield.
Repeat.

Infinite colorless mana

Ashnod's Altar

Activate Saffi by sacrificing it, targeting Extraction Specialist.
Activate Phyrexian Altar by sacrificing Extraction Specialist, adding one mana of any color.
When Extraction Specialist dies, Saffi triggers, returning Extraction Specialist from your graveyard to the battlefield.
When Extraction Specialist enters the battlefield, it triggers, returning Saffi from your graveyard to the battlefield.
Repeat.

Infinite colored mana

Phyrexian Altar

Cast Leonin Relic-Warder by paying {W}{W}.
Biotransference triggers, causing you to lose 1 life and create a 2/2 Necron Warrior token.
Leonin Relic-Warder's ETB ability triggers, exiling Extraction Specialist.
Activate Phyrexian Altar by sacrificing Leonin Relic-Warder, adding one mana of any color.
Leonin Relic-Warder's LTB ability triggers, returning Extraction Specialist from exile to the battlefield.
Extraction Specialist enters the battlefield, returning Leonin Relic-Warder from your graveyard to the battlefield.
Repeat from step 3.

Infinite artifact ETB

Infinite artifact LTB

Leonin Relic-Warder

Biotransference

Cast Leonin Relic-Warder by paying {W}{W}.
Biotransference triggers, causing you to lose 1 life and create a 2/2 Necron Warrior token.
Leonin Relic-Warder's ETB ability triggers, exiling Extraction Specialist.
Activate Ashnod's Altar by sacrificing Leonin Relic-Warder, adding {C}{C}.
Leonin Relic-Warder's LTB ability triggers, returning Extraction Specialist from exile to the battlefield.
Extraction Specialist enters the battlefield, returning Leonin Relic-Warder from your graveyard to the battlefield.
Repeat from step 3.

Activate Vampire Hexmage by sacrificing it, removing all counters from Invasion of Arcavios.
Invasion of Arcavios triggers, causing you to exile it and cast it as Invocation of the Founders.
Activate Chandra's first ability by putting a loyalty counter on it, adding {1}{W}.
Cast Flicker by paying {1}{W}, targeting Invocation of the Founders.
Chandra and Invocation of the Founders trigger, copying Flicker twice, with one copy targeting Chandra and the other targeting Extraction Specialist.
Resolve the first Flicker copy, blinking Chandra.
Resolve the second Flicker copy, blinking Extraction Specialist.
When Extraction Specialist enters the battlefield, it triggers, returning Vampire Hexmage to the battlefield from your graveyard.
Resolve the original Flicker, blinking Invocation of the Founders, causing it to enter the battlefield as Invasion of Arcavios.
When Invasion of Arcavios enters the battlefield, it triggers, returning Flicker to your hand from your graveyard.
Repeat.

Combos with "Extraction Specialist"