Bond of the Familiar

Once the spell has been cast, the effects are permanent. 

This spell forms a soul bond between the caster and a willing creature of CR 1 or lower that isn't a humanoid. The creature will become a familiar to the caster but will still have free will. 

This spell has the same uses as the Find Familiar spell but with a few alterations. The range for telepathic communication becomes infinite so long as the caster and familiar are on the same plane of existence. The familiar's Intelligence increases to 10. If the familiar drops to 0 hit points, it does not disappear as if it were a conjuration. Instead, it leaves behind its body like any other creature. This spell cannot be cast on a familiar that was created using the Find Familiar spell and will fail should the caster already have a familiar from that spell or other similar ability.

The bond is also powerful enough that the death of the caster is the only thing that will permanently kill the familiar. Should the caster perish and not be revived by a resurrection spell, the familiar will die as well and no amount of magic can bring them back. Not even spells that create undead can effect the familiar. But, so long as the caster remains alive, if the familiar is slain in battle, it can be brought back by a recasting of this spell. Also, in sharing their souls to the fullest, any curse placed on the caster will also effect the familiar, but non-magical diseases and poisons do not transfer.

This spell can only be used on one creature. Should the caster attempt to bond with another creature, the spell will fail. Even after the familiar dies, should the caster cast the spell again, it will only resurrect the original familiar. It will not create a new bond. The only thing that can break the bond between the caster and familiar is a Wish spell.

The familiar will grow in power alongside the caster. Talk to your DM about specific creatures and how they scale up in power.

Casting this spell at a higher level will increase the CR cap of the creature, but will also increase the amount of gold consumed. Should a familiar bonded by a casting of this spell at 5th level, for example, be reduced to 0 hit points, the caster will need to recast the spell at 5th level in order to resurrect the familiar. Casting the spell at a level lower than the initial bond will fail to resurrect the familiar and waste the spell slot.