Description:

Individually, cranium rats are little more than your ordinary garbage rats with the slight addition of pulsing, exposed brains on their skulls. Get them in a group, though, and they become much more dangerous - their proximity to other cranium rats creates a hive mind that grows more powerful with the addition of every rat. Their intelligence can rapidly increase to godlike level, and they gain spells and other fearsome mental abilities - and it's only by slaying numerous individual rats that you can weaken the hive mind. Best to avoid them, if at all possible.

Model:

Rat.

Abilities: magic similar to magic missiles, charm person, geldee's...

Just an idea taken from planescape, to get the ball rolling, I thought an adaptation of that would have merit has a new entity in the sewer.

Don't these already exist in the module?

I'm sure they do.

Yeah there are caster rats in the module , though they arent craniums.

Cranium rats just get more intelligent the more of them are around due to sharing of brain power. That could be scripted. (and fun)

No I'm sure there are craniums too.

Hmmm, wasn't there a contest a while back about making up a new Underdarkian creature to be featured in EFU? I have several, most of which require new models, but they all failed ;)

(Minorothes, Ogrillithids, Uberillithids, Blooaths, and several other odd creatures)