Why are you even trying? What are you trying to assign `onSwitchInPriority` to? `onSwitchIn` is an event listener, you need to have some sort of effect before that effect can listen to things. You have to answer the question, "what's doing the listening"? It can be a status, an ability, an item, a volatile status, a weather effect, etc. But once you know what's doing the listening, you attach event listeners to _that_.