[Shadow] Weapon - Shadowkin

This sword was found in the Lost Depths of Azira, fully formed within the tenebrite veins that cross the abyssal valley. An unknowable shadow entity resides in the blade's shadow, either unable or refusing to respond to any attempts to communicate. Sometimes, the shadow just stares at its wielder for hours.

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Shadowkin
Weapon (longsword), legendary (requires attunement)

The magic weapon grants a +2 bonus to attack and damage rolls made with it, and reduces any bright light in a 10-foot radius around it that isn't bright sunlight to dim light. While you hold the blade, you have darkvision out to a range of 30 feet if you don't already have it.

Accursed Shadow. When you attune to it, the weapon's sentient shadow merges with your own. Until you end your attunement to the weapon, you always cast a sentient shadow unless you're in an area of bright sunlight. The sentient shadow does not obey physics like other normal shadows, and cannot communicate ideas to you. On your turns, you can use a bonus action to telepathically command your shadow to produce one of the following effects. If you take this bonus action again, the previous command immediately ends.

• Animate. You command your shadow to change its size and shape, and move to any eligible opaque surface within 30 feet of you that is not illuminated by bright sunlight.
• Grasp. You command your shadow to fill the ground within 15 feet of you with grasping darkness, transforming it into difficult terrain. The shadows move with you. If you are not on the ground, this command fails.
• Intimidate. You command your shadow to briefly grow in size or assume a terrifying silhouette, granting advantage on the first Charisma (Intimidation) check you make until the end of your turn.
• Manipulate. You command your shadow to manipulate an object by manipulating the object's shadow, as if you had cast the mage hand cantrip. This command fails if your shadow is unable to touch the target object's shadow.
• Strike. You command your shadow to make a melee attack against a creature within 30 feet of you. Its attack bonus is the same as your bonus to hit with this weapon. On a hit, your shadow deals 1d6 necrotic damage to the target.
• Take Form. You can use a bonus action to command your shadows to condense into a gloomy semi-corporeal form, appearing in a space within 30 feet of you. It uses the statistics of a shadow, except it uses your bonus to hit using this weapon (instead of its normal attack bonus). It takes its turn immediately after yours, can't move more than 30 feet away from you, and obeys your verbal commands. The shadow form persists even when exposed to sunlight. It lasts for 10 minutes, until it is reduced to 0 hit points, or until you issue another command, after which it reverts to its original form. If your shadow's Strength Drain action kills a non-evil humanoid, it does not create a new shadow; instead, the corpse's shadow immediately merges with your shadow, and you learn any information it would freely share with an acquaintance. Such information includes general details on its background and personal life, but doesn't include secrets. Once you issue this command, you can't issue it again until the next dusk.

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Rare Variant. The rare version of this weapon lacks the Grasp, Intimidate, Strike, and Take Form options for the Accursed Shadow property.

Very Rare Variant. The very rare version of this weapon lacks the Strike and Take Form options for the Accursed Shadow property.

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DESIGN COMMENTARY

For the Rare version, this weapon is essentially a +2 weapon, plus the ability to cast mage hand while there is no sunlight around. There's some other minor properties (ish?), such as imposing disadvantage on Perception checks to see the character for those without darkvision (which is rare at this level), and short darkvision for those without it (not necessarily useful). This probably stretches to the strong side of a Rare weapon, but it's not out of the ordinary for what it is.

The Very Rare version adds an at-will Intimidation and at-will difficult terrain summon, which is useful for utility and combat. The difficult terrain is particularly effective for zoning out enemies.

The full Legendary version adds bonus damage from Strike, or bonus damage from a shadow. The shadow by itself is a weak creature, but has hit point and attack bonuses. Strength drain is such a detrimental property when it hits, up to a -2 to attacks for the rest of combat; luckily, a monster at the Legendary tier of play should easily destroy a shadow immediately afterward. This property is better suited as an information-gathering tool, delivering a final strike on a human you interrogate. All-in-all, appropriate for a Legendary tier.

The design of the sword feeds into the flavor text, in which the sword was found fully formed in the deep, made of a magical dark metal called tenebrite. I looked at a couple metal shapes for this, and settled for one that was a little spikey (selenium, I think?). The shadows cast on the ground are a little wonky, but important to immediately explaining what this sword might do.