What happens if a permanent with an 'at the beginning of the end step' trigger enters the battlefield during the end step?

When a permanent with an "at the beginning of the end step" trigger enters the battlefield during the end step, the trigger will not resolve until the next end step. This is because the event specified by the trigger condition has already occurred for the current turn, and the ability will wait to trigger for the next instance of its condition being met.

In this case, the trigger is tied specifically to the beginning of the end step, which has already passed when the permanent entered the battlefield. Triggers are only capable of firing when their conditions are satisfied, and since the end step already began prior to the permanent entering, the trigger cannot activate until a future end step occurs.

This reasoning clarifies why the other options are not applicable. They either misinterpret the timing of the trigger or incorrectly assume that the trigger can resolve immediately or that it will happen for the current turn instead of next turn. Thus, the answer indicating that it will trigger in the next end step aligns with how triggers work according to the Comprehensive Rules.