Blade of the Great Old One

Weapon (any), legendary (requires attunement)

This blade is a thin clear bottle, with a cork attached by string and winged crossguards made of glass. Inside the bottle is a swirling, black and purple mass of mysterious substance not bound to any surface, in the center of the mass is a single, unblinking, pure blue eye.

Take Form. On your turn, you can uncork the bottle and speak the name of any weapon. The ichor within the bottle will pour forth and take on the form of the named weapon.

Once the swirling mass has taken form, it must take a minute to recharge inside the bottle before it can take a new form.

Dark Origins. While you are attuned to this item, damage and attack rolls with it have a +2 bonus. It deals an additional 2d6 psychic damage on a hit.

Mental Strike. When you reduce an enemy to 0 Hit Points with this weapon, you can force them to make a DC 14 Constitution saving throw. On a failure, it has its Intelligence score reduced to 0 and falls into a catatonic state that it can only recover from through a Greater Restoration spell or a long rest. Once this feature has been used, it can not be used again until after the next dawn.

This feature has no effect on constructs, oozes or plants.

Glorious Sacrifice. You can use an action to break the bottle in your hand or on a solid surface, performing a glorious sacrifice. The bottle is destroyed and releases its encased ichor in an explosion that expands to fill a 15ft radius centered on the bottle.

The creature inside, now free, possesses the body of the sacrificer or closest creature. Whoever is possessed must make a DC 20 Constitution saving throw. On a failure, they are possessed and their soul; devoured. On a success, they are reduced to 0 hp and knocked unconscious.

Every other creature in this radius must make a DC 16 Intelligence saving throw, taking 12d6 psychic damage on a failure, and half damage on a success.

The possession aspect of this feature does not affect undead, fiends, or creatures with Legendary Resistances. Constructs automatically fail this save.

The Essence of Nightmares. If you fail 3 death saving throws, or die from damage while the Blade of the Great Old One is in your possession. The swirling mass will pour out of its container and into your body, allowing you to fight for an additional 3 rounds, after this time has passed your soul is devoured and the essence retreats back into the bottle.

Credit: Sanyokvampire on deviantart.

Blade of the Great Old One v1.0

Weapon (any), legendary (requires attunement by a creature of chaotic alignment)

This blade is a large clear bottle, with a cork attached by string and winged crossguards made of glass as well. Inside the bottle is a swirling, black and purple mass of mysterious substance not bound to any surface, in the center of the mass is a single, unblinking blue eye.

Take Form. As a bonus action, you can uncork the bottle and speak the name of any weapon, the form inside will slowly leave the bottle and use it's essence to form the spoken weapon, however, the eye will always remain inside.

The more mass needed to create a weapon, such as a greataxe or warhammer, there is less substance left inside the bottle, which in turn causes the blue colour of the eye inside to dull.

Dark Origins. While you are attuned to this item, any attack roll with it has a +3 bonus. Additionally, all regular damage dice rolls have 2 additional dice, and the blade on inflicts necrotic damage.

For example; in dagger form rather than roll 1d4 piercing damage upon a hit, you would roll 3d4 necrotic damage.

If a weapon is conjured that the user is proficient with, then their proficiency bonus is added to the attack roll. If not, then they do not do so.

Blade of the Great Old One v1.1

Weapon (any), legendary (requires attunement by a creature of chaotic alignment)

This blade is a large clear bottle, with a cork attached by string and winged crossguards made of glass as well. Inside the bottle is a swirling, black and purple mass of mysterious substance not bound to any surface, in the center of the mass is a single, unblinking blue eye.

Take Form. As a Bonus Action, you can uncork the bottle and the form inside will take the shape of any weapon you name, however, the eye will always remain inside.

The more mass needed to create a weapon, such as a greataxe or warhammer, there is less substance left inside the bottle, which in turn causes the blue colour of the eye inside to dull.

If a weapon is conjured that the user is proficient with, then their proficiency bonus is added to the attack roll. If not, then they do not do so.

Changing the weapon form after it has already taken shape takes 30 seconds to take place, and during this time the mass rescinds back to the bottle.

Dark Origins. While you are attuned to this item, damage and attack rolls with it have a +3 bonus. Additionally, all damage dealt by this weapon is psychic rather than the damage dealt by the regular form.

Mental Strike. Any enemy reduced to 0 Hit Points by this weapon has its Intelligence score reduced to 0 and falls into a catatonic state that it can only recover from through a Greater Restoration spell or any spell of similar effect.

Blade of the Great Old One v1.2