The Devil You Know

Familiars in the World of Nightwick are bestowed once a pact has been made with a demon. They evil spirits that possess the bodies of animals.  The animal depends on the demon with whom the magician has a pact. The animal will appear normal under moon and starlight but grotesque and diseased under the light of the sun. Hybrid animals, such as awful rats, or goblin-shaped humanoids are sometimes used, though these make the magician's allegiance to the Pit much more obvious to witch hunters.

The animal must be provided by the magician. It must be named, anointed with holy water (as though a child), and cared for for one moon. On the night of the moon most associated with the pact-giving demon, the magician must slay the animal.  Thereafter, they must light incense and burn 1hp worth of blood and then provide a bowl filled with half their hp in blood. The burned blood, which attracts the spirit, can be from any creature but the bowl must be from the magician.

Soon the body will begin to stir and will then move to drink the blood from the bowl. Thereafter it will be bound to the magician, granting the following benefits:

• A power dependent on the pact-giving demon (eg. a familiar from Crapoad will reveal the location of a text the magician desires , once per day).
• Each time the magician levels they gain an additional spell, taught to them by the familiar spirit.
• The familiar may be sent on errands, such as spying or gathering news. This takes 2d6 weeks, regardless of the destination, and reveals the most recent news or 1d6 rumors about the location in question.  This may also be done with items or persons.
• While they can see the familiar, the magician may switch senses with their familiar spirit.  This may be maintained as long as the magician desires, but should the magician view where a creature goes when it is sent on an errand, they must make a saving throw against spells or be maddened forever, counting as a normal-human and no longer retaining the memory to cast spells. The spirit can move away from line of sight with the caster once these senses are switched, but if the effect is broken it cannot be reinitiated until the familiar returns.
• If the familiar spirit is within line of sight of the magician, the magician has a +2 to saving throws.
• The familiar may act as instructor in languages or other minor, non-weapon proficiencies, taking the same amount of time as a normal tutor but without the need to pay gold. 

However, having an evil spirit as a companion also imposes a number of problems:

• Each day the magician must feed the familiar spirit 1hp worth of blood or it will become temporarily powerless.  Should it go without, the next time it feeds it shall drain 1hp per day that was missed, even if this kills the magician.  
• A magician with a familiar may not be resurrected from the dead. In addition beneficial clerical magic only works on them 50% of the time, unless it is cast from a scroll or another item in which case it is always effective (except raise dead).
• Should the familiar spirit be destroyed, the magician immediately loses 4 levels of experience. Should this cause them to be slain, they disappear in a cloud of greasy, black smoke.

A familiar spirit will never use its attack in defense of its master, only itself, but may cast spells on their behalf; however, they only do so rarely, since if the magician dies their soul is sent to the Pit and the familiar spirit's evil mission completed.

Regardless of the type of animal they resemble, all familiars have the following statistics.

FAMILIAR SPIRIT

AC 2 [17], HD 2+2, Attk 1 (1d8 + poison), THAC0 16 [+3] MV 180' (60') Flying, SV D8 W9 P10 B10 S12 (7), ML (special), AL Chaotic, XP 1,650 NA 1 (1) TT Nil

• Mundane Damage Immunity: Familiar spirits may only be hit by weapons which are silvered or +1 or better.

• Deadly Poison: The bite of a familiar spirit, regardless of the form it takes, causes a saving throw verses poison or die.
• Spell casting: At will the familiar spirit may cast detect good, invisibility, and detect magic. Once per week they may commune with the beings of the Pit.

• Weakness to Daylight: A familiar spirit may neither fly nor benefit from its mundane damage immunity while the sun shines upon it.

• Piggy-back: Once per month, the familiar may carry the magician or a person they designate upon its back.  It may then fly tirelessly for an entire night.

If you want an interesting form for your familiar, head over to my patreon and check out the most recent post to see the Awful Rats with stats for OSE and art by Chris Huth.

Edited to include some critiques from Gavin Norman, author of OSE.