Activate Ashnod's Altar by sacrificing Yosei.
When Yosei dies, it and Gift of Immortality trigger.
Resolve the Yosei trigger, causing the next player in turn order to skip their next untap step.
Resolve the Gift of Immortality trigger, returning Yosei from your graveyard to the battlefield.
At the beginning of the end step, Gift of Immortality triggers, returning it from your graveyard to the battlefield attached to Yosei.
Repeat during each turn unless you are the next player in turn order.

Opponents skip their untap steps

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Yosei, the Morning Star

Gift of Immortality

Ashnod's Altar

Activate Ashnod's Altar by sacrificing Yosei, adding {C}{C}.
When Yosei dies, Nim Deathmantle triggers, causing you to pay {4} to return Yosei from your graveyard to the battlefield, and attach Nim Deathmantle to it.
When Yosei enters the battlefield, it triggers, causing target opponent to skip their next untap step, and tapping five permanents that opponent controls.
Repeat for each remaining opponent, and during each of your turns.

Nim Deathmantle

Activate Phyrexian Altar by sacrificing Yosei, adding {1}.
When Yosei dies, Nim Deathmantle triggers, causing you to pay {4} to return Yosei from your graveyard to the battlefield, and attach Nim Deathmantle to it.
When Yosei enters the battlefield, it triggers, causing target opponent to skip their next untap step, and tapping five permanents that opponent controls.
Repeat from step 1 for each remaining opponent.
Repeat for each remaining opponent, and during each of your turns.

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