Effect
Once per turn, during each player's Standby Phase: The turn player declares a Level from among the face-up monsters they control, then sends all face-up monsters they control with a different Level to the Graveyard.
The activation of the card "Unification of the Heavens" can be performed at any time, except during the Damage Step.
The effect "During each player's Standby Phase, the turn player chooses 1 Level among the monsters they control, and sends all other face-up monsters they control with a different Level to the Graveyard" is an effect that starts a Chain Link. (It does not target.)
When activating the card "Unification of the Heavens" during your or your opponent's Standby Phase, you can also activate its effect in the same Chain Link as the card's activation.
The effect of "Unification of the Heavens" is a mandatory effect that activates once every time a Standby Phase (yours or your opponent's) occurs. (It also activates and starts a Chain Link if there are no face-up monsters, or if there are only face-up Xyz or Link Monsters.)
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