You attempt to implant an organ, limb or other body part from a CR 3 or less creature into another voluntary creature you touch.

Target a voluntary creature and make an intelligence check with a DC determined by the DM based around the state of the body part (damaged, old, pristine, etc) your familiarity with the creature to which the body part belongs (for example, most people are more familiar with the physiology of a beast than an aberration) and the level of precision it requires to implant it (an organ such as a gland or an eye is usually more difficult than a limb). A non-organic body part such as the arm of a construct cannot be used by this spell.

On a successful check, the body part is assimilated by the target and it gains all the abilities that said body part granted to the creature. For example the beak of an owlbear may grant you their beak attack, the skin of a displacer beast their natural armor and displacement traits or the liver of a troll their regeneration, speak with your DM to decide the nature of the abilities, if they are specific to one body part and the specifics on how to use it. The organ or limb used merges with the target's body, so a target does not for example have to lose his previous arm to gain a new one and can choose whether the new arm will fuse to his previous one or just be added as a third arm.

On a failed check the Target takes 1d8 slashing damage and 2d8 necrotic damage, and its hit point maximum is reduced by 3d6, this condition can be cured by a greater restoration spell.

The assimilated body part lasts for the duration or until you cast this spell again, when the spell ends the assimilated body part falls to the ground or is vomited if it was inside the creature's body, and it can't be used by the spell again.

This spell can also be used to reattach lost limbs, in which case the caster has advantage on the check and the effects of the spell become permanent (it does not heal hit points)

 At higher levels. When you cast this spell using a slot of 7th level or higher, the CR of the creature you can assimilate goes up by one for each slot level above 6th