Cast Sidisi from your graveyard by paying {3}{B}{B}.
When Sidisi enters the battlefield, its exploit ability triggers, causing you to sacrifice Sidisi.
Sidisi's second ability triggers, causing you to search your library for Nexus of Fate and put it into your hand.
Cast Nexus of Fate by paying {5}{U}{U}, causing you to take an extra turn after this one and shuffle Nexus of Fate into your library.
Repeat each turn.

Infinite turns

Lock

Gisa and Geralf

Sidisi, Undead Vizier

Nexus of Fate

Cast Sidisi from your graveyard by paying {3}{B}{B}.
When Sidisi enters the battlefield, its exploit ability triggers, causing you to sacrifice Sidisi.
Sidisi's second ability triggers, causing you to search your library for Beacon of Tomorrows and put it into your hand.
Cast Beacon of Tomorrows by paying {6}{U}{U}, causing you to take an extra turn after this one and shuffle Beacon of Tomorrows into your library.
Repeat each turn.

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