I know they're really not popular and so I'll probably never see them again but Imaginary Friends. Maybe this time if they could be optional instead of by chance so people could more easily opt out if them if they don't want them, and those that do can guarantee them.
They were my favourite by far, second being mermaids. What I loved about Imaginary friends is they were an occult really focused on kids. All the other occults don't really kick in until they're grown to at least teens, but imaginary friends was all about those young ages. It was a built in playmate and you could still enjoy them when your sim was an adult, and make them real if you wanted! For someone who really likes occults and family play, it was a great balance that actually let me do the super natural things with my child sims instead of just waiting for them to age up to enjoy the benefits. Just lots of story possibilities with an imaginary friend that you didn't even have to make an official sim if you didn't want too.
