A small house cat gently purrs and twitches its tail. Suddenly it lets loose a blood-curdling yowl as it arches its back. An illusion gives way to the true creature: a rotting undead cat with glowing green eyes, long teeth, and claws like knives.

Yowlers are undead house pets and familiars with a score to settle and a hatred of the living.

Mistreated in Life. Many house pets and familiars have terrible masters who mistreat the animals in life. When these creatures die (often as part of the master's mistreatment), night hags find the animals' souls and send them back to inhabit their bodies. The soul re-enters its old vessel, resulting in the creation of a yowler, an undead creature with supernatural powers, a burning desire for revenge on its old master, and a hatred of all living creatures.

Illusionary Mask. Unless a yowler has recently acted violently, illusionary magic makes it appear to look as it did in life. Once the yowler attacks, its true form is revealed: that of a rotting corpse with green eyes, long claws, and envenomed fangs.

Necromancer and Night Hag Familiars. After a yowler has taken its revenge on its former master, a necromancer or night hag might find and adopt the yowler as a familiar. The yowlers' illusionary masks make the creatures excellent spies, and they are tougher than the average familiar. While these masters may show affection to their yowlers, the undead pets still harbor a hatred for all living creatures, including those to whom they are currently bound.

Undead Nature. The yowler doesn't require air, food, drink, or sleep.