Ebony Blade

The Ebony Blade is the legendary sword of Sir Percy of Scandia, gifted to him by Merlin. It is cursed by the blood that its original wielder shed. It had the most use under the many individuals under the moniker Black Knight.

History
Merlin, a powerful Mystic, came upon the Starstone, a black material from a fallen meteor. He imbued it with powerful magic able to reflect magical attacks. It was for a time wielded by the Knights Templar, as well as a Valkyrie.

Curse
The Ebony Blade is cursed to possess the user should it's might be used to kill a person with a certain. Should it go over 20 Evil Points, the blade's passive and active actions will cease to function and the wielder will roll with disadvantage on attack rolls made with the weapon. The Evil Points can be cancelled through Greater Restoration or a similar artifact.

Passive
Magic Resistance: The wielder gains resistance to all damage dealt through magical means or weapons.

Rending: Should the artifact or weapon not have the 'Power Immune' passive ability, this artifact can cut through it, ignoring resistances and immunities and decreases AC by 1 for every attack. If targeting a weapon, the user must succeed on a DC 15 save to not have their weapon broken.

Power Immune: The artifact is immune to all effects and powers not cast by the wielder. This doesn't extend immunity to the wielder. It cannot be broken, transported (seperately from the wielder), or altered by an opponent.

Last Laugh: The artifact allows the wielder to automatically succeed on death saves and gain 10 health points once per day. You gain this ability again after completing a long rest.

Active
Reflect: As a reaction, you can make a 20 Dexterity check to reflect a magical attack back toward the attacker. They must make a Dexterity check not to take full damage. On a success, they take half damage.