A familiar is a mage's kindred spirit, bonded to their very life energy. In most cases, the familiar is an ordinary animal whose personality somehow mirrors the mage's own, and is thus called when the mage casts Find Familiar. 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.
The mage receives various benefits from their familiar - some are simple, others more difficulty to penetrate. They receive a +1 bonus to surprise rolls whenever their familiar is close by due to their companion's heightened 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. Your familiar cannot read a book for you and recite it back, but it could tell you approximately where it is. Finally, the mage receives something of the heightened sense of their familiar - a bird's eyesight, a cat's nightvision, a wolf's sense of smell - et cetera.
Once bonded, the mage and their familiar must remain together always. They can be apart for up to a day without incident, but if they go longer than this the link will being 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.
Familiars are usually animals that have been "ascended" by the familiar bond - usually, but not always. In some cases, supernatural or extraplanar entities of a petty nature might choose to bond to a wizard's life force. As there is usually some element of summoning or calling involved in these cases, finding these kinds of familiars is more complicated - often requiring the casting of a spell such as Ensnarement or a ritual such as Karna's Invocation.
There are a variety of creatures a mage may summon to be their familiar, depending on their alignment. Imps and quasits suit those of evil alignment - both will make their caster more powerful and may share infernal secrets with them, and neither can be permanently destroyed on the Material Plane (see the Monstrous Manual for a full description of the benefit's conferred by an imp or quasit). Both have agendas of their own, however, and regard their masters more as clay to be sculpted than as their superiors.
Less darkly aligned mages may instead opt for other creatures of minor supernatural provenance, such as petty faeries. In cases such as these, it is up to the DM to determine the nature of the bond and what benefits the mage receives. Supernatural familiars, as a general rule, will always confer more power than mere bonded animals.
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 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.