A familiar must be more than a mere house-cat. Magic should be weird, and there is nothing weird about owning a pet. A witch is more than a cat lady. Here is how I would rule a player character obtaining a familiar. Do I fall into the trap of old school referees who “at best might homebrew some … procedure to feel better about” players obtaining a pet? Maybe, but this procedure is cool, so it’s worth it, I swear.

First, I would remove the “Find Familiar” spell entirely. There is no need to impose a spell tax just to get a familiar. Instead, you must complete a ritual. Witchcraft, as opposed to more humdrum magic, is better with a ritualistic aspect, not just some spell components you can handwave (perhaps literally in the case of somatic components). In this case, the ritual is inspired by Gu, a folkloric poison-magic associated with the ancient kingdom of Nanyue. 

Only a person capable of casting magic spells can begin a ritual to obtain a familiar. Preferably a member of a coven of magic users, but wizards are known to have familiars as well. To obtain a familiar, you must capture two animals that are small enough to fit together in a caldron, preferably made of brass. Add a drop of your own blood to the caldron to bind the familiar to you. Then seal the creatures together in the caldron and light a fire underneath the caldron using charcoal, herbs, incense, and fat. Wait 1d6 x 10 minutes (or 2d6 dungeon turns if in a dungeon) then open the lid. If performed under the light of a full moon or on the fifth day of the fifth month, the time for this ritual is halved. At the end of the ritual, one of the animals will have killed the other. You may flip a coin to determine which prevailed.

The victorious creature shall emerge from the caldron as your familiar, although it is altered in body, mind, and spirit. Most obviously, it appears as the victorious animal with one aspect of the animal that perished in the caldron. For instance, it may be a black cat with the tail of a scorpion, a hawk with the eyes of a toad, a lizard with the wings of a bat, a weasel with the tentacle of an octopus, etc. If you aren’t sure what aspect from the deceased creature should be incorporated into your familiar, get suggestions from the rest of the players at the table and pick. The ultimate combination of body parts is up to the player whose character performs the ritual. 

Legend has it that the first owlbear was created by a powerful wizard engaged in this ritual, but the resulting creature proved too powerful to bind to their service and thus killed the spellcaster. It is for this reason that familiars are typically no larger than a dog. That and the impracticality of finding a caldron large enough to fit a bear.

Your familiar behaves as if permanently under your charm and will perform any task you assign it to the best of its ability. The familiar has the intelligence of a bright child, can understand language, and can even carry on conversations if normally capable of speech (such as parrots) or sign language (such as monkeys). Some practitioners have been known to place the severed head of a recently deceased humanoid in the cauldron, which causes the familiar to be able to speak in a roughly human voice, but has the side effect of a 4-in-6 chance of giving the familiar humanoid features (e.g., the face of a human on a cat, the ears of a human on a raven, or the hands of human on a spider). Your familiar has its own personality but is always bound by the laws of magic to serve you at any cost.

Additionally, you and your familiar are linked telepathically, allowing telepathic communication so long as you are on the same plane of existence. When you close your eyes, you can choose to see what your familiar sees. You still smell and hear what is around yourself. You can always sense what direction your familiar is from you even if you cannot see it, so long as you are on the same plane of existence and the familiar isn’t protected by any anti-divination magic.

Familiars have a number of mechanical benefits and a few drawbacks. When you cast a spell with a range of touch, your familiar can deliver the spell as if it had cast the spell, so long as the familiar is within your line of vision. The familiar shares the magic user’s pool of hit points. If the magic user’s hit points fall to zero, in addition to the impact this has on the magic user, this causes the familiar to disappear in a burst of fire. A familiar that has disappeared for this reason may be resummoned from hell by expending 1 spell slot and burning incense and a vial of your tears in a cauldron for 1 hour. Each time you perform this ritual, your appearance changes slightly in line with the appearance of your familiar. For instance if your familiar is a black cat with the tail of a scorpion, your hair may turn black as night the first time you resummon your familiar, you may gain cat eyes the second time, cat ears the third time, etc. Each change is purely cosmetic and at the discretion of the magic user’s player. A magic user may only ever have one familiar, so performing the ritual to gain a new familiar means you can no longer resummon a lost prior familiar, condemning them to an eternity in hell. If ever a magic user dies, their familiar dies with them. 

The connectivity between a magic user and their familiar has been taken advantage of by unsavory witch-hunters. For instance, a witch-hunter who captures a magic user’s familiar can torment the magic user from afar by harming its familiar. 

Based on the primary form of your familiar, the magic user gains access to one spell. You can cast this spell innately without the need for a spellbook so long as your familiar is within your line of sight. Some of these spells are from Cairn’s base spells or Cairn’s list of d666 spells. A couple were made up wholecloth. If you have a familiar of some other type, browse the list and select a spell that fits the character of the creature.

Several other bloggers have tackled this topic before me. If my familiar thoughts have only roused your imagination without properly bedding it down, you may want to check out:

You’re Doing Familiars All Wrong, GOBLIN PUNCH

Find Familiar - rewrite, SHOUTING INTO THE VOID

A Familiar Problem, FRACTALBAT

Familiar Binding, Redux, TOMB OF THE WANDERING MILLENNIAL 

D100 Familiar Features, D4 CALTROPS

I’m Not Familiar, TALES OF THE LUNAR LANDS

Familiars, RISE UP COMUS