Weapon (falchion), legendary (requires attunement by a creature of neutral alignment)
Cataract is a uniquely-crafted falchion with a segmented, fully rectangular blade, similar to that of a cleaver. The entire weapon is forged in pure, pitch-black obsidian metal. In the weapon's hilt is embedded a yellow, crystalline cat's eye, which swivels and tilts under its own power as Cataract observes its surroundings through it.
You gain a +3 bonus to attack and damage rolls made with this magic weapon. It has the following properties.
As a bonus action, you can press the trigger embedded into Cataract's handle to separate and extend its segmented blade parts, transforming the weapon into a heavy, bladed whip. In this form, Cataract has the reach and finesse weapon traits, and its damage die is reduced to 1d6. You can spend a bonus action to press the trigger again at any time to retract Cataract's blade back into its original form.
You may spend an action in combat to have Cataract cast the Mirror Image spell on you, creating three shadow clones of yourself. Once all three clones are destroyed or dismissed, Cataract cannot use this ability until after your next short rest.
Cataract is a consummate history buff, and will readily share its knowledge when the situation calls for it. You have proficiency and advantage on all history checks while you are attuned to this weapon.
Sentience. Cataract is a sentient true neutral weapon with an Intelligence of 18, a Wisdom of 14, and a Charisma of 12. It has hearing and darkvision out to a range of 120 feet.
The weapon can speak, read, and understand Common, and can communicate with its wielder telepathically. While you are attuned to it, Cataract also understands every language you know.
Personality. Cataract possesses the soul of a lone wolf from a past age, a learned young outcast who often worked in the shadows. In spite of its ability to communicate, Cataract is normally calm and reserved, and doesn't talk much, preferring to speak through the actions of it and its wielder. When it does speak, it prefers not to take ideological sides, preferring to simply focus on getting the current job done. It is a moderate in all things, and does not have a high opinion of extremists of any stripe.
Cataract is more willing to open up regarding the subject of history and literature. It is a bookworm at heart, and is always on the lookout for new historical lore, and actively requests to preserve literature found in dangerous places that it might find interesting. It will even request to read such texts together with her wielder, if only to continue fulfilling its love of reading. If Cataract goes seven days or more without finding new historical lore, a conflict between the blade and its wielder occurs at the next sunset.
Cataract also has a secret weakness for smutty literature, to the point where it can sense where such literature might be located nearby. It will sometimes try to subtly direct its wielder towards locating examples of smut, under the guise of looking for historical texts. Unfortunately, this makes its assistance in searching for historical literature somewhat unpredictable, much to its secret shame.