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 ETB

Infinite LTB

Infinite sacrifice triggers

Falkenrath Forebear

Voldaren Bloodcaster // Bloodbat Summoner

Phyrexian Altar

Anointed Procession

Activate Krark-Clan Ironworks by sacrificing a nontoken artifact creature, adding {C}{C}.
When the creature dies, Voldaren Bloodcaster and Nim Deathmantle trigger.
Resolve the Voldaren Bloodcaster trigger, creating a Blood artifact token.
Activate Krark-Clan Ironworks by sacrificing the Blood token, adding {C}{C}.
Resolve the Nim Deathmantle trigger from step 2, causing you to pay {4} to return the artifact creature from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Repeat.

Nim Deathmantle

Krark-Clan Ironworks

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.

Combos with "Voldaren Bloodcaster // Bloodbat Summoner"