The ahuizotl is a vicious, semi-aquatic predator that resembles a hideous cross between a badger and an otter, with disturbingly web-fingered paws supplemented by a fifth hand at the end of a long, serpentine tail. A clever and stealthy hunter, the ahuizotl lures unwary prey to their doom by mimicking the cries of people in distress. The ahuizotl's macabre habit of feeding on a victim's eyes, fingernails, and teeth leaves the corpses of its kills uniquely mutilated. Some say the creatures consider these body parts delicacies, while others insist ahuizotls collect them as tribute to a powerful but unknown entity. The fact that an ahuizotl does not eat the actual flesh of its victims, instead depositing their savaged and waterlogged corpses in locations where the remains are sure to be found by friends or family, points to a third and perhaps more likely possibility—the ahuizotl simply enjoys using its violent dietary quirks to spread fear and despair.

An ahuizotl walks on all fours, but its hands are capable of manipulating simple tools and other objects. Ahuizotls have roughly mustelid features and an extra membrane covering their eyes, giving their eyes a dull color suggestive of cataracts and somewhat blunting the creature's vision. Yet despite their bestial appearance, ahuizotls are nearly as intelligent as the average human, and wiser than most. Although they don't form societies of their own, they have been known to ally with violent cults or conclaves of monsters, and even to found small shrines and temples to sinister deities. The cult of Charon, the horseman of Death, is particularly popular among certain ahuizotls, who look forward to an afterlife spent wallowing in the waters of the River Styx.