What four bosses are on the Difficult Boss Battles Mount Rushmore?

Board 8

I played Pokemon GSC more than a dozen times
I have never, ever, whatsoever had any problems with Whitney
But maybe that's because I always play solo starter so by the time I reach her it's extremely overleveled (might even be a 3rd stage evolution but idk)

-Yellow Devil (Megaman 1)
wololo