The familiar is a being - usually an animal, but sometimes a wholly supernatural entity - that is spiritually bonded to the mage it calls "master". The power of this bond is of benefit to both familiar and master, but it carries with a dependence that can be dangerous to both if broken. Regardless of what type of familiar you seek, the Find Familiar spell is used both to summon a suitable creature and to bind it to you.
Although there are some specific benefits that depend on the type of familiar you have (detailed below), there are some general benefits and drawbacks to being bonded to a familiar. A mage receives a +1 bonus to surprise rolls whenever their familiar is close by due to their shared senses, and in turn confer their saving throws on the familiar when they are close to it. They also have an empathic link with their familiar that functions at a distance of up to 1 mile. While you cannot see through their eyes or speak directly with words, the link is complex enough to give orders, receive warnings and generally communicate.
Once bonded, the mage and their familiar must remain within 1 mile of each other always. They can be apart for up to a day without incident, but if they go longer than this the link will begin to shrivel and wither. The familiar loses hit points at a rate of 1 for each day they are apart from their master. When their hit point total drops to 0, they will die. If the familiar dies in this way, or in any other, their master will permanently lose a point of Constitution. Conversely, the death of the master will immediately kill the familiar.
The most common familiar is an ordinary animal such as a cat, owl or rat, which is conjured simply by burning 10 GP worth of incense and casting Find Familiar. Any natural, non-magical creature can be bonded, but they can be no larger than a wolf and can possess no magical powers. They must also be of animal intelligence. The spell does not "teleport" the animal to the spellcaster - instead, it calls out to a nearby animal within one mile. If the caster desires a specific animal as a familiar, they may include a desirable offering in the incense brazier. For example, to summon a raven familiar, the caster would include something shiny such as silver pieces.
Both master and familiar benefit from the spiritual bond that is forged between them: the familiar becomes far more intelligent than a normal animal of its kind, gaining 2-3 points of INT. They also have a far longer lifespan than animals of their type usually do. They also receive 1 additional hit point per level of their caster; if their natural AC is worse than 7, it becomes 7.
Natural familiars also confer something to their masters that other types of familiars do not; heightened senses. For example, a wizard bonded to a cat may gain excellent night vision and superior hearing - imposing a penalty to attempts made to surprise them and giving them an almost infravisual ability.
If the prospective master desires a familiar with greater powers and deeper insight, they may choose to seek out a supernatural being to serve as their familiar. Not all magical creatures are eligible; creatures such as pseudodragons, brownies and pixies are good examples of supernatural familiars, but a dragon or manticore would be wholly inappropriate. At the end of the day, it is the DM's decision. At the very least, the supernatural familiar must be intelligent; you cannot bond a magical beast such as a manticore.
As with natural familiars, the desired supernatural being must be within 1 mile when you cast Find Familiar. Although it is not required, it is strongly recommended that you bring some sort of offering to improve the being's disposition - for a brownie, this might be bread, milk and honey. You must still burn 10 GP worth of incense when casting the spell; this will send out a summons that will almost always bring forth a curious specimen of the desired creature, if one is in range.
Unlike an animal, supernatural beings get a say in whether they will become your familiar. Plying them with gifts is a good start; the Find Familiar spell also gives them an insight into your alignment and personality, so they must like what they see. Only once they are willing to become your familiar can they be bonded by the spell.
For the most part, supernatural familiars function the same as the more mundane type, though they don't get the Intelligence, bonus hit points and AC that animal familiars do. This is more than made up for by the magical powers they possess, however - a supernatural familiar is a useful companion to their master indeed.
Finally, creatures from other dimensions can be made into familiars. This is by far the most difficult option, because the Find Familiar spell cannot reach across the planes. The first hurdle is summoning the creature in the first place. This can be done with a spell such as Ensnarement or a summoning ritual. In the case of creatures eager to be made into familiars, such as imps, it may be enough to simply invoke them by their name.
Once the magic-user has successfully summoned a planar being, they may cast Find Familiar with the usual incense offering and attempt to bond it. As with supernatural familiars, the summoned creature must be intelligent and it must agree to become a familiar. However, the caster has a little more leverage here; just as you can compel a summoned creature to serve you by imprisoning it in a magic circle until it relents, you can compel it to agree to be your familiar. It is far wiser to bargain with a creature you are planning to soulbind, however; a surly familiar is more trouble than it is worth. Note that becoming a familiar is restrictive and potentially dangerous to a creature, so it is unlikely that powerful extraplanar beings will ever agree to become one.
For the most part, extraplanar familiars are the same as supernatural ones, but there is one key difference. Assuming they hail from the Outer Planes, death is not permanent for them. They can only be permanently killed on their native plane; if slain anywhere else, they will eventually reform on their home plane. They can then return to their master; or, if they lack the power to plane shift, they can be summoned by their master. This also allows them to survive their master's death; a planar familiar whose master dies will only have their physical form destroyed.
This does not make them invincible, however. There is always the chance that the familiar will suffer some misfortune on their home plane before they have a chance to return to their master. They also suffer from the same dependence as other familiars: they must stay within 1 mile of their master. If they leave their master - being stranded on their home plane counts - they will slowly waste away and eventually die. This death is permanent, and so becoming a familiar always carries some risk.
As natural spirits or supernatural outsiders, a familiar is naturally more attuned to the spirit world than their mortal masters. Although the benefits they confer on their masters and their effectiveness as spies or scouts is undeniably useful, this is the true role of a familiar: to act as the link between their master and the mysteries of the multiverse. Familiars have a natural affinity and understanding of such things, and can often act as guides and advisors to the spirit world, even through their limited empathic link.
In certain circumstances, a familiar can even go beyond the role of an advisor and sounding board on all things immaterial. In some cases, they can even call upon their bond to the master's spirit to pull their dreaming soul from their body and into the Ethereal or Astral. Of course, they will not (and often cannot) do this on command. An extraplanar familiar will do this only when it serves their own ends. An animal familiar will not consciously know how to do it at all. They are driven by instinct, and only when the time is right and the need is great will they do what must be done.
A familiar is not a small burden, nor is it a temporary alliance. Tied to the very life force of the spellcaster, their role evolves over their career: at first a guide, then a companion, then a faithful assistant. Although their powers grow to assist their master, so too does their connection to his life force. Many mages choose not to keep their familiar forever - a choice that is not taken as an affront by their companion, who knows their energies could be expended at guiding another rather than following a mage who does not need them.
At first level, each familiar gains an ability that is relevant to their role as a guide in their master's life. This power is up to the discretion of the DM and player, but will always be relevant to the familiar' most important duties. Examples include:
- If a tiny spider in the ear acts as a source of restraint and wisdom for an overly spontaneous mage, the ability to detect magical and spiritual vibrations (in a vague way) will be helpful in dispensing advice.
- For a raven whose master is always surrounded by enemies, the ability to speak with their avian brethren may help in gathering intelligence.
Once the master reaches 5th level, a difficult choice must be made. The familiar's role as a guide into the dangerous world of magic has ended, and they must decide whether to maintain their bond or allow their familiar to move on. If they choose to remain together, their bond will become even more powerful. This occurs at the 5th, 7th and 9th levels of experience. Each time, the special abilities of their familiar will grow in power in a manner deemed appropriate by the DM. However, the corollary is that their strengthened bond is even more dangerous to break: each time it is strengthened, the number of points of Constitution lost by their familiar's unnatural death will increase by 1.
Note that the rules given above apply only to familiars obtained at level 1; if a master obtains a familiar later in his career, all of the milestones below his current level are "skipped". A level 5 wizard who obtains a familiar will find that their new companion is identical to a 1st-level familiar, albeit with more hit points. However, they will continue to gain new powers at levels 7 and 9.
Eventually, the tenuous fragility of a familiar bond is overcome. In order for their familiar to ascend, the wizard in question must be at least 12th level and must have spent at least 5 of those levels bonded to his familiar; the familiar must also be a natural animal. Supernatural and extraplanar beings cannot ascend. Ascension is the ultimate manifestation of the familiar bond: transcending their mortal form, the familiar becomes an astral being that cannot be permanently slain outside of the Astral Plane.
The ascension of a familiar has no obvious effects until the familiar in question is reduced to 0 hit points. When this happens, they will not die: instead, their body is reduced to a mist that quickly dissipates, their consciousness sent to prowl the Astral Plane. In their place is left a small gemstone statuette about an inch high: a Figurine of Wondrous Power.
The newly ascended familiar cannot die in battle; whenever they die, they revert to a figurine as they return to the Astral to recuperate. Here, their wounds heal at a rate of 3 hit points each day. Likewise, they can also be commanded to return to the Astral at any time their master desires, reverting to figurine form. They may be recalled at any time - even directly after being defeated - although a heavily wounded familiar will be of little use.
The ascended familiar is not without risks, however. Ascension is how Figurines of Wondrous Power are made; anyone who kills the master and takes it gains control over the familiar. Although the familiar will not have the same empathic bond with its new master, it will obediently obey any commands given to it. The master must be killed, however, for this to work; simply taking the figurine will not be enough as long as the familiar bond still exists. If the statuette is not claimed by a new master within an hour of the wizard's death, it shatters and the familiar is no longer able to be recalled from the Astral.
Note that the familiar still remains a free-willed individual of its own. If its master mistreats it, it may refuse to come forth when summoned from the figurine. It may even choose to return to the Astral, leaving its figurine behind and refusing to return until proper amends are made. This does not apply to figurines taken from their original masters, however - they must obey their new owners regardless of how they feel.