Shadow Steel Claymore

Another deadly invention, but not by gnomes, Shadow Steel is said to require souls to be produced. According to rumors, the souls are torn into pieces using dark spells and transformed into a raw spiritual essence of pain, which takes a pitch-black sheen reflecting no light. Weapons made from it cannot be resisted by conventional metals. They cut through the spiritual essence of living flesh, discharging excruciating pain into the victim. The rare survivors of these weapons report levels of pain that can render a person inert for hours. When wielding a weapon made of Shadow Steel, you have advantage on attack rolls made against any target wearing medium or heavy armor. A creature hit by a Shadow Steel Blade must make a DC 14 Constitution saving throw, becoming stunned until the end of its next turn on a failed save.

Brutal: A brutal weapon is designed for maximum damage. When you score a critical hit with a brutal weapon against a creature, you can roll an additional die of the weapon's damage dice, adding it to the damage total.

Heavy: Creatures that are Small or Tiny have disadvantage on attack rolls with heavy weapons. A heavy weapon's size and bulk make it too large for a Small or Tiny creature to use effectively.

Two-Handed: This weapon requires two hands to use. This property is relevant only when you attack with the weapon, not when you simply hold it.

Proficiency: martial, greatsword Source: Source: Grim Hollow: Campaign Guide p. 216 (Third Party), Grim Hollow: Player's Guide p. 131 (Third Party)