You control at least one other non-Human creature.
Mana Needed
({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
Yahenni by sacrificing
Nethroi.
When
Nethroi dies,
Pitiless Plunderer triggers, creating a Treasure artifact token.
Resolve the
Yahenni ability, giving it indestructible until end of turn.
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
Yahenni twice by sacrificing
Eternal Witness and
Mitotic Slime.
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.
Resolve both
Yahenni abilities, giving it indestructible until end of turn.
Activate
Yahenni twice by sacrificing two Oozes.
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.
Resolve both
Yahenni abilities, giving it indestructible until end of turn.
Activate
Yahenni twice by sacrificing two Oozes.
When the Oozes die,
Pitiless Plunderer triggers twice, creating two Treasure artifact tokens.
Resolve both
Yahenni abilities, giving it indestructible until end of turn.
Activate the seven Treasures by tapping and sacrificing them, adding ({4} magic symbol) ({GW} magic symbol) ({B} magic symbol) ({B} magic symbol) .