Activate Phyrexian Altar by sacrificing Falkenrath Forebear, adding {B}.
When Falkenrath Forebear dies, Voldaren Bloodcaster triggers, creating two Blood artifact tokens.
Activate Falkenrath Forebear by paying {B} and sacrificing the Blood tokens, returning it to the battlefield from your graveyard.
Repeat.

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Falkenrath Forebear

Voldaren Bloodcaster // Bloodbat Summoner

Phyrexian Altar

Anointed Procession

Activate Shilgengar's first ability by sacrificing Falkenrath Forebear, 
When Falkenrath Forebear dies, Pitiless Plunderer triggers, creating two Treasure tokens.
Resolve the Shilgengar ability, creating two Blood tokens.
Activate a Treasure by tapping and sacrificing it, adding {B}.
Activate Falkenrath Forebear by paying {B} and sacrificing the two Bloods, returning Falkenrath Forebear from your graveyard to the battlefield.
Repeat.

Infinite artifact ETB

Infinite artifact LTB

Infinite artifact sacrifice triggers

Infinite artifact tokens

Infinite colored mana

Infinite Treasure tokens

Shilgengar, Sire of Famine

Pitiless Plunderer

Activate Phyrexian Altar by sacrificing Falkenrath Forebear, adding {B}.
When Falkenrath Forebear dies, Voldaren Bloodcaster triggers twice, creating two Blood artifact tokens.
Activate Falkenrath Forebear by paying {B} and sacrificing the Blood tokens, returning it to the battlefield from your graveyard.
Repeat.

Drivnod, Carnage Dominus

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