Prepare For Trouble, Make It Double
While Team Rocket's James makes strides in the WVGCW as the most dangerous manager ever to grace the pseudo-pseudo-sport, I figured we'd take a look at famous duo bosses from the world of video games. These guys always attack as a pair, and whether their skills reflect or complement each other they've created some memorable boss fights in upping the challenge by coming at you simultaneously.
Well, I say "I figured", but this was @video_game_king's idea. He did suggest tag team bosses, but it's harder to come up with a list where boss characters alternate their assault outside of Fighters. We won't be covering any Fighters in this list, for the record. Too easy. I've also tried to shy away from boss fights where you're fighting two carbon copies of the same creature, or multiple clones a la Pinwheel or Fool's Idol. I tend to favor the "complementary polar opposites" set-up, because it's an interesting scenario to balance for a designer.
But as always, this list is representative rather than comprehensive, so there'll be many instances of this particular boss fight set-up I either forgot or haven't encountered personally. That's what the comments are for, you wonderful helpful VG aficionados. Do my work for me.