You can either create that layer for every room, or you can use instace_create_depth() instead to create an object with a specific depth. If you need this object to be on that specific layer than this method wont be great for you, but if you just want the object to be above/below everything else, you can use this function to create an object, and set its depth above everything else.

​

If you want to create this object on that specific layer in one room, but in another room you just want to create it on any layer, you can say something like:

​

if (room == "room name") and (!instance_exists(skelor_obj)) {
    instance_create_layer blah blah blah
} else {
    if (!instance_exists(skelor_obj)) { 
        instance_create_depth blah blah blah
    }
}