Darkness, the King of Dark, is blessed with extraordinary beauty, a powerful and varied set of abilities, and genius level intellect. He's also a mean bastard that keeps curb-stomping our heroes into oblivion whenever they met. But at least he looks good in leather pants...
Parodied: Darkness is absurdly powerful but he's also overly hilarious, and extremely wacky, so people (both in-universe, and audience-wise) like to have him around just to see what kind of amusing shenanigans will he come up with next.
Zig Zagged: King Light is insanely powerful, trashing all who oppose him. But in a straight-up fight with the heroes, he gets completely thrashed by The Power of Friendship, and his secret benefactor strips him of all his lent powers in disgust. Busted down to lowly Mook status, he promptly makes a meteoric rise through the ranks on his own strength, earning back his gifted powers... just in time to get slammed back down by the heroes in a Curb-Stomp Battle.
Averted: King Light appears to be tough but he's defeated for real on his first appearance.
The writers want an absurdly powerful villain to build up anticipation, and sales, for his inevitable defeat.
The programmers wanted King Light to be That One Boss, and made Darkness, the King of Dark a super-powerful Bonus Boss.
Lampshaded: "Isn't there anything you can't do, Darkness?!" "Yeah, I cannot be humble about it, pathetic fool!"