Find Familiar is a Conjuration spell, currently used by Potentia both as a ritual spell and as part of her PhD studies. The spell is only available to Wizards but also requires fairly expensive materials to cast.
The character gains the service of a familiar, a spirit that takes an animal form they choose: Bat, Cat, Crab, Frog (or toad), Hawk, Lizard, Octopus, Owl, Poisonous Snake, Fish (quipper), Rat, Raven, Sea Horse, Spider, or Weasel. Appearing in an unoccupied space within range, the familiar has the stats of the chosen form, though it is a celestial, fey, or fiend (player choice) instead of a beast. A summoner can't have more than one familiar at a time. If this spell is cast while they already have a familiar, the familiar can adopt a new form from the above list.
The familiar acts independently of the character, but it always obeys their commands. In a combat situation, it rolls its own Initiative and acts on its own turn. A familiar can't attack, but it can take other actions as normal. When the familiar drops to 0 Hit Points, it disappears, leaving behind no physical form. It reappears after the spell is cast again.
While the familiar is within 100 feet of its summoner, they can communicate with it telepathically. Additionally, as an action, they can see through their familiar's eyes and hear what it hears until the start of their next turn, gaining the benefits of any special senses that the familiar has. During this time, the character is deaf and blind with regard to their own senses.
As an action, a familiar can be temporarily dismissed by its summoner. It disappears into a pocket dimension where it awaits their summons. Alternatively, a familiar can be dismissed forever. As an action while it is temporarily dismissed, the summoner can cause their familiar to reappear in any unoccupied space within 30 feet of them.
Finally, when the summoner casts a spell with a range of touch, their familiar can deliver the spell as if it had cast the spell. The familiar must be within 100 feet of the summoner, and it must use its reaction to deliver the spell when it is cast. If the spell requires an attack roll, the payer uses their attack modifier for the roll.