What happens to a legendary permanent if another of the same kind enters the battlefield?

In the context of Magic: The Gathering, when a legendary permanent enters the battlefield, the legendary rule comes into effect. This rule states that if a player controls two or more legendary permanents with the same name, they must choose one to keep, while all others are put into their owner's graveyard.

Therefore, if another legendary permanent of the same kind as one already on the battlefield enters, it triggers this rule, leading to only one of those permanents remaining in play. The remaining one is determined by the controlling player, who will select which one to keep based on their strategy or preference, and all others must go to the graveyard.

This interaction highlights the unique characteristic of legendary permanents that distinguishes them from non-legendary permanents, which can coexist without restriction. The correct answer accurately reflects the application of the legendary rule in this situation.