Linus was a Borne prototype, a consciousness residing in a golem-like construct.

You gain a +2 bonus to attack and damage rolls made with this adamantine magic weapon. When you hit a construct with this weapon, that creature takes an extra 2d6 force damage.

Project Consciousness

When you hit a construct with this weapon you can use a bonus action to temporarily transfer Linus into the target (DC 12 Charisma saving throw). Linus is overcome by the target's original orders (she doesn't act as an ally) but the presence of a mind means the target loses any condition immunities to being charmed and frightened, and any damage immunity to psychic damage. Linus returns at the end of your next turn. During this time, the weapon loses all properties except for being made of adamantine. Once used, this property can’t be used again until the next dawn.

Overwhelm 

When you score a critical hit with this weapon against a construct, you can choose to leave Linus stuck inside the target (no action needed). The target becomes an ally under your command. At the end of each of its turns, it can make a DC 14 Intelligence saving throw to push the alien presence out; on a success, the weapon falls to the ground at its feet. You can choose to end the effect earlier by drawing Linus from the construct's body, as a bonus action.

 

Sentience

Linus is a sentient lawful neutral weapon with an Intelligence of 13, a Wisdom of 6, and a Charisma of 9. It has hearing and darkvision out to a range of 60 feet.

The weapon communicates telepathically with its wielder and can speak, read, and understand Common and Primordial.

Personality

Linus wants to be a "good golem", and is judgmental of all other constructs. It is vengeful and suspicious, but easily distracted.

Proficiency with a longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Risuri, Damage, Buff, Debuff, Combat, Sentient, Versatile