Memento of the Shapeless (Patreon)

Weapon (any melee weapon without the reach or heavy property), legendary (requires attunement)

This weapon was forged using the preserved remains of an ancient mimic. You gain a +2 bonus to attack and damage rolls made with this magic weapon.

As a bonus action, you can speak the weapon’s command word to reshape it into ( * ) any melee weapon with which you’re proficient that does not have the reach or heavy property.

When you hit a creature with this weapon, you can also attempt to grapple it (save DC 13) by channeling the weapon’s natural pseudopod form. While grappling a creature in this way, you can’t attack or grapple another. Releasing the weapon frees the creature.

Pseuperpod. As an action, choose a creature within 30 feet and make a melee attack against it using the weapon. The weapon stretches towards your target as a pseudopod, ignoring half and three-quarters cover, and deals 6d8 bludgeoning damage if it hits. After the attack, the weapon retracts back into its previous form. If you attempt to grapple the target with the attack, the save DC increases to 15 for this attack. If the creature fails, it is dragged up to 15 feet closer to you before being released from the weapon’s grasp. If it failed the saving throw by 5 or more, it is dragged up to 30 feet closer to you and remains grappled. Once you’ve used this feature, you can’t use it again until 12 hours have passed.

Limb replacement. If you’re missing an arm or forearm, you can graft the weapon to you in its place. If you do, the weapon changes and reforms to match the missing limb. You can add your proficiency bonus to any Strength (Athletics) checks you make using the limb, or double the bonus if you’re already proficient. You can alter the arm’s form to turn it into a weapon as needed.

Forged by the legendary dwarven hero Harrun Withermount, a powerful warlock of his time, after a fruitless adventure into the catacombs under the lost city of Farrel. He and his companions had spent days in its cells fending off monsters and horrors the likes of which have yet to be seen since. At long last, they found the chest they'd heard of and sought. When the chest bit back, though, Harrun lost his temper. And his arm.

In the end, though, he got back at the beast...as well as his missing limb.