En Holl
From CloudModding OoT Wiki
ovl_En_Holl is the actor used for invisible room transition planes, making it possible to seamlessly swap out rooms
Notes
ovl_En_Holl performs a very odd and specialized check. On every frame, it will check to see if the current entrance index is set to 00EE (Kokiri Forest cutscene), and the scene setup is 8 (cutscene 4). When these conditions are met, ovl_En_Holl will indefinitely keep both rooms that it links to loaded simultaneously once the camera comes close to the transition.