Whenever an opponent controls a creature, activate Ashnod's Altar by sacrificing Keiga, adding {C}{C}.
When Keiga dies, it and Nim Deathmantle trigger.
Resolve the Keiga trigger, causing you to gain control of a creature an opponent controls.
Activate Ashnod's Altar by sacrificing the creature you gained control of in step 3, adding {C}{C}.
Resolve the Nim Deathmantle trigger from step 2, causing you to pay {4} to return Keiga from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Repeat as desired and/or whenever a creature enters the battlefield under an opponent's control.

Gain control of all creatures opponents control and sacrifice them

Gain control of any creatures that enters the battlefield

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Keiga, the Tide Star

Nim Deathmantle

Ashnod's Altar

Whenever an opponent controls a creature, activate Phyrexian Altar by sacrificing Keiga, adding {1}.
When Keiga dies, it, Pitiless Plunderer and Nim Deathmantle trigger.
Resolve the Pitiless Plunderer trigger, creating a Treasure artifact token.
Resolve the Keiga trigger, causing you to gain control of a creature an opponent controls.
Activate Phyrexian Altar by sacrificing the creature you gained control of in step 3, adding {1}.
When the creature dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Activate the Treasures by tapping and sacrificing them, adding {2}.
Resolve the Nim Deathmantle trigger from step 2, causing you to pay {4} to return Keiga from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Repeat as desired and/or whenever a creature enters the battlefield under an opponent's control.

Pitiless Plunderer

Phyrexian Altar

Whenever an opponent controls a creature, activate Thermopod's second ability by sacrificing Keiga, adding {R}.
When Keiga dies, it, Pitiless Plunderer and Nim Deathmantle trigger.
Resolve the Pitiless Plunderer trigger, creating a Treasure artifact token.
Resolve the Keiga trigger, causing you to gain control of a creature an opponent controls.
Activate Thermopod's second ability by sacrificing the creature you gained control of in step 3, adding {R}.
When the creature dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Activate the Treasures by tapping and sacrificing them, adding {2}.
Resolve the Nim Deathmantle trigger from step 2, causing you to pay {4} to return Keiga from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Repeat as desired and/or whenever a creature enters the battlefield under an opponent's control.

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