Battletoads was perhaps the hardest game ever on the NES and BTBM on the SNES was also quite hard, though not as much. The game was shorter, and honestly didn't do to much more than the first game did. Still, it was good and in classic Rare style as well, back when they made good games for Nintendo instead of shitty ones for Microsoft.
It's a shame the series has never been revived. There exists a video for an alpha version of Battletoads Advance, but as you can guess, the game was canceled thanks to Microsoft. Even though the only video does look suckish, it was an alpha, so it's likely the game would've gotten better if development continued.
But of course, we can't even count on the original games being released on Virtual Console, again, thanks to Microsoft, they're forbidden too unless it was an XBLA exclusive, and that's bullshit! Rare was at their best with Nintendo, and games that should be on the Wii VC, like the Banjo series, are on the 360 instead.
Okay, I'm done ranting. Enjoy a piece of music from a better time.