Activate Ashnod's Altar by sacrificing another creature, adding {C}{C}.
The creature dies, triggering Pitiless Plunderer, creating a Treasure token.
Activate Karn by paying {1}, causing the Treasure to become a 1/1 artifact creature until end of turn.
Repeat.

Infinite colorless mana

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Karn, Silver Golem

Pitiless Plunderer

Ashnod's Altar

Chief of the Foundry

Activate Krark-Clan Ironworks by sacrificing another creature, adding {C}{C}.
The creature dies, triggering Pitiless Plunderer, creating a Treasure token.
Activate Karn by paying {1}, causing the Treasure to become a 1/1 artifact creature until end of turn.
Repeat.

Krark-Clan Ironworks

Activate Phyrexian Altar by sacrificing another creature, adding {1}.
The creature dies, triggering Pitiless Plunderer, creating a Treasure token.
Activate Karn by paying {1}, causing the Treasure to become a 1/1 artifact creature until end of turn.
Repeat.

Phyrexian Altar

Activate Krark-Clan Ironworks by sacrificing Sword of the Meek, adding {C}{C}.
Sword of the Meek dies, triggering Slagstone Refinery, creating a tapped Powerstone token that enters the battlefield as a 1/1 creature due to March of the Machines and Chief of the Foundry.
Sword of the Meek triggers, returning itself from your graveyard to the battlefield, but not attaching itself to the Powerstone due to Sword of the Meek becoming a creature.
Repeat.

Infinite tapped creature tokens

Infinite tapped Powerstone tokens

Slagstone Refinery

March of the Machines

Sword of the Meek

Activate Ashnod's Altar by sacrificing Sword of the Meek, adding {C}{C}.
Sword of the Meek dies, triggering Slagstone Refinery, creating a tapped Powerstone token that enters the battlefield as a 1/1 creature due to March of the Machines and Chief of the Foundry.
Sword of the Meek triggers, returning itself from your graveyard to the battlefield, but not attaching itself to the Powerstone due to Sword of the Meek becoming a creature.
Repeat.

Combos with "Chief of the Foundry"