Sworn enemy.

Against Dungeon or Academy, Cursed One is needed to quickly eliminate enemy troops, so as not to allow the enemy Hero to severely damage you with magic. So, it should be upgraded regardless of the opponent; it is a real help in battle.

Not only against Dungeon and Academy, but for everyone. You should always try to eliminate enemy troops as quickly as possible. Why did the developers reward the Sylvan army with such a good unit? If you have the opportunity, use it!