I beat Battletoads on NES once, and that was brutally hard. The only game I played and wasn't able to beat was Ghosts 'n Goblins. You had to go through the game twice to beat the final boss and going through just once was impossible.
both are brutal I beat ghosts and goblins which I thought was easier than battletoads only because toads keeps throwing you curveballs in gameplay whereas goblins is always straight forward, but picking up a bad weapon in ghosts and goblins is nearly as bad as resetting the game accidently. You need the shield to kill the level 6 and 7 bosses