I'm not sure how canon the instructions are necessarily, but like, in my mind | like to think that Slither somehow found out that Oz sometimes just stays at school late and falls asleep there and that's where he's sleeping when they meet each other and like, even back when they were enemies, Slither legitimately got pissed at him for it.
Like Slither is attacking some Dream Realm with Nightmare Creatures when Oz comes to stop him and at some point during the fight Slither just goes, "Are you sssleeping at work again?" and then just immediately completely stops the fight and orders the Grimspawn not to do anything until Oz goes back to his house and sleeps there because Oz is not a worthy opponent if he isn’t in fighting shape because I definitely feel like falling asleep in an uncomfortable place would probably have some kind of ramification in the Dream World since it’s established that sleeping when you don’t need to makes it hard to stay there already.
