Trey and Troy, the "bad" Dimensional Guardians from the web fiction serial Dimension Heroes often pick fights with the protagonists.
In the Global Guardians PBEM Universe, The ambitious and brutal Blackstar was thrown out of the Guardsmen, the intergalactic superhuman police force, and is now the sworn enemy of the heroic Guardsman, defender of Earth.
The Tyrants are a "mirror universe" version of the Global Guardians.
1d4chan has created an epic inversion with Brighthammer 40k, a reimaging of Warhammer 40,000 that replaces the Grimdark future of Warhammer 40k with a bright happy Star Trek-esque universe where the everything is going great and instead of war, there is only HIGH ADVENTURE. Essentially, it takes Warhammer 40k from the cynical side of the scale and slams it down to the idealistic side.
In Worm, the Villain Protagonist Skitter realizes that the Slaughterhouse Nine, a team of psychotic superpowered serial killers, are essentially this to her own Noble Demon team, the Undersiders. They rely upon hit and run tactics and pick their battles with utmost care, striking only to cause maximum damage at minimum risk to themselves, and deliberately tailor their tactics to induce as much fear as possible.
Skitter: The Nine are us on steroids.
In The Cartoon Man, Simon becomes Roy's evil counterpart when the same black ink that caused Roy's cartoon transformation turns him into a mustache-twirling cartoon villain.