True Familiar

This spell can only be cast as a ritual, and can only be understood and cast by Artificers, Bards, Druids, Sorcerers, Wizards and Warlocks.   Through the casting of this spell, you call out to the world around you and the DM will choose what creature responds to your call if the spell is successful.  

The spell is successful using the following formula:  An Animal Handling roll, with a DC of 20, minus both the character's charisma modifier and their spell casting class level.  For example, a character with a charisma 16 casting the spell as a 9th level wizard (20-3-9=8) needs to roll at least an 8 to succeed.  If the caster takes additional measures that he/she feels will improve the success of the spell, such as offering specific foods, or pledges, or promises of power, the DM may choose to allow the player to have an advantage on their roll.  If the player is trying to call a specific type of animal, or even one animal in particular, the DM might expect the character to take extra-ordinary measures to ensure their success, such as by offering specific types of food, or casting the ritual while in the presence of a specific animal.  Note, if the animal they are specifically attempting to call is under any type of duress, such as unwilling captivity or having suffered in any way at the hands of the spell caster, the DM is within their rights to declare that the spell is cast at a disadvantage.  Succeed or fail, in either case the materials are obviously consumed.

DM's must use the following to determine what creature responds to your call:  1) The creature should generally be found in the area where the spell is cast (i.e. hills, forest, swamp, urban, coastline)  2) The level of the caster is taken into account, where higher levels will call a creature (animal/monster/magical) with a higher challenge rating.  The creature will always be of a size small or tiny, but may be a smaller version of larger animals (such as a tiny unicorn or a "small" bear - these may be creatures that have wandered in from the fey wild or the shadowfell).  Smaller creatures of what are usually large animals will, of course, have adjusted stats and capabilities.  3) The distance over which the caster's influence may cover will depend on the level of the spell caster, where a low level wizard may only be able to call creatures in the immediate area, and a 15th level Druid may call a creature from 20 miles away, or maybe even from another plane.  4) Creatures will increase in intelligence with higher level casters (it is perfectly reasonable for a 15th level Druid to call a creature capable to speech and intellectual thought.)  5) DMs should try to match the character's alignment and personality when choosing a creature.

The ritual spell, if successful, will give the caster one point of exhaustion, and should usually be cast before taking a long rest.  This will also give the called creature an opportunity to present itself.   Even then, the DM may choose that the animal takes longer to respond (to give the DM time enough to determine what creature responds to the spell)

Just so you understand, the creature that responds to your spell is an actual creature, not the spirit form of that creature.  It will have the abilities of the creature, whether natural or magical.  They are a real creature, subject to their own abilities and flaws, and maybe even personalities.  An intelligent familiar may offer its own opinion about events/decisions facing the spell caster, even if the caster does not wish to hear those opinions.  In combat situations, the creature will always follow immediately after you in the initiative order, and will act on its own turn.  The creature is capable of attacking enemies, which it will gladly do in defense of you unless you have specifically told the creature to stay out of the battle.  Your familiar acts independently of you, but it usually obeys your commands. The greater the creature's intelligence and abilities, the more likely it is that it will do whatever it feels is necessary to defend you.

When your familiar responds to your call, its hit points are added to your hit point total, and you and your familiar will now share this hit point pool.  Damage taken by either of you will be taken from this pool, except in the case of an area affect where both of you are present and hit.  In this case, the damage is only taken from the pool once.  When both the caster and the familiar drop to 0 hit points, the familiar will also drop to unconsciousness and will eventually die if not assisted.  In the same way, if assistance is given to either the caster or the familiar, both will be revived.  After the initial exhaustion of the spell is taken care of, you will then gain an advantage whenever rolls are made to determine if you are exhausted or not, if the familiar is within 100 feet of you.

While your familiar is within 100 feet of you, you can still communicate with it telepathically.  Unlike arcane familiars, however, you are not able to see or hear through your familiar's senses, unless the creature has an intelligence of less than 4 AND a Beast Sense Ritual has been cast.  Also, unlike arcane familiars, you are not able to dismiss your familiar into any type of pocket dimension, unless the ability comes from some other source.

You cannot have more than one familiar at a time. If you attempt to cast this spell while you already have a familiar, the spell will automatically fail (and your current familiar will likely not be very happy with you).  However, you can choose to dismiss a familiar, which usually happens when as spell caster attains higher levels.  This is done for both the safety of the creature and to obtain a higher level of familiar.  Dismissing the familiar requires that the spell be cast with this goal in mind, though there is no pass/fail DC roll for it to succeed.   NOTE: a familiar will never forget its relationship with you and will always have its empathetic link with you, but the hit point bond and telepathic connection are broken, and the familiar will leave in pursuit of its own life.

Finally, similar to an arcane familiar, if you are able to cast a spell with a range of touch, your familiar can deliver the spell as if it had cast the spell itself. Your familiar must be within 100 feet of you, and it must use its reaction to deliver the spell when you cast it.  However, if the spell requires an attack roll, the creature must use its own attack roll for a successful hit.