While the illithid might not be common across the planes, these servitors of Ilsensine certainly are. Today, the cranium rat, a pest throughout Sigil and abroad.
A pest across the planes, the cranium rat is a vermin with a secret. A strange sight, these look like nothing more than common rats with the tops of their skulls lopped off, letting their brains pulse out through them. However, cranium rats are in fact the eyes and ears of the god-brain Ilsensine, spread throughout the planes to gain ever more information for the power. Though a few hives do fall out of its control, most notably the Us of Sigil, in general these vermin serve as one of many information-gathering sources for the great deity of the illithid. Few are aware of these origins, however, and even fewer survive to inform others once they discover the truth.