where did the Horrorterrors come from? any ideas on that? also why are there barely any dead alpha kids and beta kids in the dream bubbles? the trolls are the ones with the most ghosts but there aren't many of the kids or even cherubs

The Horrorterrors are just a force of Paradox Space much like Skaia is. It’d bet he same as asking ‘Where did SBURB come from?’, it’s just part of Paradox Space, Elder Deities hovering the outskirts of the Universe.

As for the Dream Bubbles, there are multiple reasons but, well, think that Karkat’s group spent a few weeks and there were 1000 Aradiabots, and the Dancestors spent years in the Session. The Betas were in their Session for 1 single day, and the Alphas had to spend nearly half a year, but said half year was incredibly uneventful. Not many points where a Timeline can split when you spend so little time and there’s not much to do.