If two legendary permanents with the same name enter the battlefield simultaneously, what happens?

The "legend rule" (CR 704.5j) is a state-based action checked continuously. It states: if a player controls two or more legendary permanents with the same name, that player chooses one to keep and puts the rest into their owners' graveyards.

When two legendary permanents with the same name enter the battlefield at the same time — for example, via a mass-reanimation spell — the game checks state-based actions after the event resolves. At that point, both copies exist simultaneously, triggering the legend rule. The controlling player must choose one to keep; the other goes to the graveyard. If each copy is controlled by a different player, each player independently keeps their own — the legend rule only applies within a single player's control (CR 704.5j).

It is important to note that "enters the battlefield" triggers (if any) still fire for both permanents before the legend rule removes one. State-based actions are checked after triggers are placed on the stack, so both ETB triggers happen regardless.

Concrete example: You cast Finale of Devastation and fetch two copies of Emrakul, the Promised End from your library, putting both onto the battlefield. State-based actions are checked: you control two legendary permanents named "Emrakul, the Promised End." You choose one to keep; the other is immediately put into your graveyard.

Key rules: CR 704.5j (legend rule state-based action), CR 704.3 (state-based actions checked after each event), and CR 603.6 (ETB triggers still happen before SBAs remove a permanent).