Are there any "rules" for familiars? Suggestions for witch of doom??? Or all of the witches? Also witch of void would have nothing?

I mean, they seem Aspect-related. Other than that? Go wild really. Familiars are hard to come up with not because they’re limiting but because. Just. What do you use. It could be anything. It could be someone, something. It could be an entity they worship or they could be their best friend. It could be an Eldritch Abomination or their Pet Dog. :Ic