I've been really enjoying the passive mob variants added by quark, and I'd like more of them! The main thing I would like out of this is more slime variants, but I think color variants for some of the newer mobs, like allays and sniffers, or some of the other classic hostile mobs, like endermen, ghasts, and blazes could also be fun. There are also some passive mobs with limited utility like squid and bats that might benefit from a little attention to make them add a little more detail to the world.