Winter's Dark Bite

You have a +1 bonus to attack and damage rolls made with this magic weapon. This greatsword is made of an unknown black metal. In most cases, it works as a +1 greatsword. But when used against a thessalhydra, it works as a +3 greatsword. While in the Upside Down, it works as a +4 greatsword.

Two-Handed: This weapon requires two hands when you attack with it.

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.

Proficiency: martial, greatsword Source: Hunt for the Thessalhydra p. 4