Cranium rats are minions of mind flayers, created “by bombarding normal rats with psionic energy” (and also, it seems from the illustration, delicately removing the top layers of their scalp and skull). Mind flayer colonies use them as forward observers; although the range of their telepathy is short (only 30 feet), the 120-foot telepathic range of a mind flayer extends their link to a more practical distance, and the 5-mile range of an elder brain increases their effectiveness by several orders of magnitude.
A lone cranium rat can’t do much. It’s extremely weak, with only 2 hp and 30 feet of darkvision. Its Bite attack is inconsequential. It can cause its brain to glow, emitting eerie dim light to a range of 5 feet, but that’s not very useful. If its range were 30 feet, it could combine this illumination with its darkvision to eliminate its Perception penalty within that radius. Since its passive Perception is only 10, that would be fairly useful. At only 5 feet, though, all a single cranium rat can do with this glow is give itself away.
However, a cranium rat that’s actively spying for a mind flayer colony might be ordered to use Illumination because a mind flayer or elder brain wanted to get a good, clear look at someone or something that the cranium rat had approached in the dark. In this scenario, the cranium rat is effectively doomed to die, providing a brief moment of extreme creepiness before it succumbs to an opportunity attack. If that attack should somehow miss, the cranium rat snuffs its light and Dashes away, hopefully to safety. Continue reading Cranium Rat Tactics