Leaving one room and entering another, in GameMaker's order:

1. leaving: every instance's room end event; then every instance that is not persistent runs its clean-up event and is removed
2. entering: each instance the room places, in the room's order, is created — its pre-create and create events — and runs its own creation code; an instance whose id is already present (a persistent one) is not placed again
3. in the game's first room, every instance's game start event
4. the room's creation code

An instance a GameMaker Studio 2 room places on an instance layer takes that layer's depth, and is marked as on it (room_layer).

5. every instance's room start event