Symbiont-Intelligence Gland

This appears as a smooth liver-like organ that sprouts tendrils and forces itself into one of the host body's orifices and implants itself somewhere near the brain or spine.

Once embedded, the symbiont provides an Intelligence boost as well as the ability to add 1d4 to any knowledge based proficiency check once per long rest. It understands Deep Speech but can speak telepathically with its host once bonded. 

Symbiotic Nature - This cannot be removed while you are attuned to it, and you cannot voluntarily end your attunement to it. If you are targeted by a spell that ends a curse, your attunement to it ends, and it leaves your body.

Notes: Bonus: Intelligence Score, knowledge based proficiency boost, Death Saving Throw