Nupperibo

Nupperibos technically rank higher than Soul shells and Lemures, though that doesn't mean they get to boss them around or anything; they're as mindless as the larvae that they grow from. It doesn't mean they're stronger than the lemures either: most are
actually a little weaker. What it means is that they're slightly more magical than lemures are, and they tend to be a little rarer (that there's only so much room at the top is a fundamental baatezu law).

When they get too common, they're melted down into lemures (seeing as they've already proved themselves far stronger than most Larvae) or sold to the Yugoloths who, as they are observed to fear their potential as much as the Baatezu high-ups do, can be trusted to consume
them.

There are actually two kinds of nupperibo. The kind most see is entirely faceless and featureless, looking like a star-shaped blob of boneless flesh. More rarely, you can pick out one with vague hints of eyes, ears, fingers or mouths - whether this means it's evolving into something greater, or if it just means the larva it came from was once a mortal soul instead of a stray piece of evil drawn out of the substance of the plane is something I don't know.

Sometimes a nupperibo is the reborn spirit of a powerful baatezu killed off-plane. These
belong to the first type, never having any distinguishing features at
all. See also Baatorian.