Darkside is the first true enemy that Sora faces in his adventures and the largest Heartless in the series’ first game in the franchise. He is especially difficult since the first game was far more difficult than Kingdom Hearts II and the fight with him is pretty much the first fight
you get into in the series.
Darkside appears at the Dive to the Heart, Destiny Islands, and makes his final appearance in the first game at the End of the World. Each fight is more difficult than the last and his giant stature and Shadow spawning powers ensure that it is never a fight between just you and him. He is memorable, unique and to say he is strong would be an understatement.