A very dangerous property on tough melee fighters, this one increases the damage for the boss and his whole minion pack.
Extra Strong is one of the attributes that Unique Monsters may spawn with in Diablo II. This attribute is a physical attribute, since it affects the damage the monster does.
Monsters with the extra strong attribute will do 2.5 times more damage, and their minions will do 1.75 times more damage. Obviously this can be devastating when put onto a very hard hitting monster like a Blunderbore, and not that threatening when put onto a monster that uses magic as its main attack, like a Black Soul.