Eternal Witness and Mitotic Slime in your graveyard.
Pitiless Plunderer and Phyrexian Altar on the battlefield.
You control at least one non-Human creature.
({4} magic symbol) ({GW} magic symbol) ({B} magic symbol) ({B} magic symbol) plus enough mana to pay for commander tax, if applicable available.
Steps
Cast Nethroi either from your hand or from the command zone for its mutate cost by paying ({4} magic symbol) ({GW} magic symbol) ({B} magic symbol) ({B} magic symbol) plus commander tax, if applicable, putting it on top of a non-Human creature you control.
When Nethroi enters the battlefield, it triggers.
Holding priority, activate Phyrexian Altar by sacrificing Nethroi, adding one mana of any color.
When Nethroi dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Resolve the Nethroi trigger from step 2, returning Eternal Witness and Mitotic Slime from your graveyard to the battlefield.
When Eternal Witness enters the battlefield, it triggers, returning Nethroi from your graveyard to your hand.
Activate Phyrexian Altar by sacrificing Eternal Witness and Mitotic Slime, adding two mana of any color.
When Eternal Witness and Mitotic Slime die, Pitiless Plunderer triggers twice and Mitotic Slime triggers once.
Resolve both Pitiless Plunderer triggers, creating two Treasure artifact tokens.
Resolve the Mitotic Slime trigger, creating two 2/2 Ooze creature tokens.
Activate Phyrexian Altar by sacrificing two Oozes, adding two mana of any color.
When the Oozes die, they each trigger and Pitiless Plunderer triggers twice.
Resolve both Pitiless Plunderer triggers, creating two Treasure artifact tokens.
Resolve both Ooze triggers, creating four 1/1 Ooze creature tokens.
Activate Phyrexian Altar twice by sacrificing two Oozes, adding two mana of any color.
When the Oozes die, Pitiless Plunderer triggers twice, creating two Treasure artifact tokens.
Activate the seven Treasures by tapping and sacrificing them, adding ({4} magic symbol) ({GW} magic symbol) ({B} magic symbol) ({B} magic symbol) .