What happens when a second planeswalker of the same type enters the battlefield?

When a second planeswalker of the same type enters the battlefield, the rules state that a player can only have one planeswalker of each specific name under their control at any given time. This is enforced by the "planeswalker uniqueness rule," which is found in the rules governing planeswalkers.

According to this rule, when a second planeswalker of the same name enters the battlefield, the original planeswalker and the newly entered one must be placed into the graveyard simultaneously. This is the reason why the correct answer highlights that all instances of planeswalkers of that name are put into the graveyard.

This scenario provides a clear and defined resolution, ensuring that the game maintains the uniqueness of planeswalker cards on the battlefield, which directly impacts strategic play within the game.