This function can be used to destroy all the instances assigned to the given layer. You supply the layer ID (which you get when you create the layer using layer_create()) or the layer name (as a string - this will have a performance impact), and then all instances that are on the layer will be removed from the game, triggering their Destroy and Clean Up events.
|layer_id||The unique ID value of the layer to set the depth of (or the layer name as a string)|
Real (Unique ID value for an instance)
The above code will check a global variable and if it's true then all instances that are on the layer of the calling instance will be destroyed (including the calling instance).