Blade of R'lyeh (5e Equipment)
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This sword has ornately sculpted tentacles wrapping around the handle, and detailed engravings of suffering and madness on the guard. It was forged by the ancient aberrant servants of Cthulhu, and appears to be in motion when viewed from the corner of one's eye.
You gain a +3 bonus to attack and damage rolls made with this magic weapon. It also deals an additional 1d10 psychic damage on a hit. You can use your Charisma modifier in place of your Strength or Dexterity modifier for this weapon's attack and damage rolls. If you use Charisma, the damage bonus is in psychic damage. You must use the same modifier for both rolls. This sword ignores resistance to piercing damage, along resistance and immunity to psychic damage.
Will Breaker. When you hit a target with this weapon, it must succeed on a Charisma saving throw against your spell save DC or become frightened of you for 1 minute. In addition, the target can't take reactions for the duration. They may repeat the saving throw at the end of their turn, and if they succeed they are no longer frightened. If you roll a 20 on the die for an attack roll made with this weapon, the target is considered to be paralyzed until the start of your turn.
His Likeness When you attune to this weapon green, leathery wings sprout from your back, granting you a flying speed of 50 feet if it isn't higher already. You gain a swimming speed of 20 feet if it isn't already higher, and you can breathe underwater. If you have 17 or more levels in the warlock class, you gain resistance to necrotic damage.
Awareness. While wielding this weapon, you are aware of all creatures within 60 feet of you, and you know their type and size category. You can telepathically communicate with any aberration within 60 feet of you. This requires no action. You can telepathically communicate wit Cthulhu anywhere. You know Deep Speech and Primordial.
Dark Tentacles. While wielding this weapon, as a bonus action, you can create shadowy tendrils from any area of dim light or darkness within 30 feet of you. These tendrils automatically attack any creature of your choice within 10 feet of them at the start of your turn. They have an attack and damage bonus equal to your Charisma modifier, and they deal 1d6 bludgeoning + 1d6 necrotic damage on a hit. The tendrils disappear after 1 minute. The blade regains use of this property at dusk.
Curse. When you attune to this weapon, your alignment changes to Lawful Evil. In addition, you hear voices in your head that urge you to kill. At the end of every long or short rest you take, roll a d12. You must kill a number of non-evil creatures equal to the number you rolled. If you don't kill them with this weapon, you gain no experience points from them. If you take a rest before killing the creatures, make a DC 20 Charisma saving throw. On a failure, your hit point maximum is reduced by 1. If it is reduced to 0, you die. You cannot tell anyone else about any properties of this curse. While attuned to this item, you cannot attune to any good magic items (Holy Avenger, Book of Exalted Deeds, etc.) Your alignment can't be changed in any way. A Remove Curse spell must be cast as 9th level to break your attunement to this item.