Watching The Omen trilogy last week has inspired me to attempt statting up Damien's guard dog, the demonic "hellhound".
DEMON, THE HOUND OF HELL
#ENC: 1 (unique)
HD: 8 (56)
AC: 0 
Atk: claw, claw, bite (1d8, 1d8, 1d12) + special
- MIND CONTROL: If the Hound Of Hell gets surprise on its victim, it may - once a day and only on one, sentient, target - attempt to "mind control" its prey, in lieu of a physical attack. The target must make a Save vs Charm Person. If they fail they will be compelled to acts of elaborate, delusional violence, either against themselves or another (possibly while declaring fealty to the dog's master). The subject is allowed to make a WIS save to try and break the spell every time he is about to commit violence (e.g. attacking another, causing harm to themselves). A failure means they carry through the act. Once the spell is broken, that person can never be controlled in this way again by the Hound.
- CONTROL THE ELEMENTS: Once per day, in lieu of a physical attack and only when the dog is outdoors, it is able to conjure mighty winds and a lightning storm within a 200ft radius. This will last for 2d4 rounds. All (except the dog) caught up in this must save vs STR each round to avoid being blown over by the unnatural winds. For the duration of the storm, the dog also gains a bonus attack, which he still needs to roll for: a lightning bolt from the sky, which causes 8d6 damage (save for half) if it hits.
- IMMUNITY TO NON-MAGICAL ATTACKS: Only magical spells and enchanted weapons can cause harm to this demon, and it's also immune to any form of mind-control magic, charm, sleep etc.
This large, muscular Rottweiler-like dog is dispatched from the depths of Hell to stand guard over a particular devil or demon operating on the surface world.
If not by his master's side, he will be out doing his bidding (which is usually eliminating threats).