Corrupted Sword

Evil Aura. Any creature that touches the sword or hits it with a melee weapon wile within 5 feet of it takes 5 (1d10) necrotic damage. 

False Appearance. While the sword remains motionless, it is indistinguishable from a normal decaying sword.

Possession. If a creature picks it up, the sword attempts to possess that creature as described in the Possess Sword attack.

Multiattack. The sword makes two slash attacks.

Slash. Melee Weapon Attack: +# to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) slashing damage plus 2 (1d4) necrotic damage.

Possess Sword (1/Day). The sword attempts to possess a creature within 5 feet that is  wielding a weapon that deals slashing damage. That creature makes a DC 15 Charisma saving throw. On a failed saving throw, the sword transfers its corruption to the weapon  and takes control of its wielder. It retains its alignment and Intelligence, Wisdom, and Charisma scores. Its stats are otherwise replaced by the wielder's. On a success, the sword takes 21 (2d10) force damage.