Hazardous (X)
From Archon Arcana - The KeyForge Wiki
When a creature with the hazardous X keyword is attacked, it deals X damage to the attacking creature before the fight resolves. (The activeplayer chooses whether this occurs before or after other “Before Fight”effects and keywords.) If this damage destroys the other creature, therest of the fight does not occur.
If a creature with the hazardous (X) keyword gains another instance of the hazardous (X) keyword, the two X values are added together.