Q!Slime would serve the entity of the Desolation because he is very self destructive, he suffers from the loss of his family and is easily angry when seeing happy families (the Desolation likes to destroy people's lives with great potential) and literally went on a rampage to avenge his daughter which was often portrayed with fire (atleast his stream vods' miniatures have a LOT of fire). This is less directly related but the Desolation is associated with wax, the followers have wax skin, which reminds me of Charlie's, well, slime appearance.
The Lonely fits him as well because he lives in exile, often says crowds are too much for him (might not be in the lore but oh well) and his exile home is near the sea so its prone to mist.