Games for the Nintendo Entertainment System have a reputation for being brutally difficult compared to today's products (heck, even the generation that followed the NES lightened up slightly), but one of the most challenging and outright unfair games from the old days is Rare's Battletoads which kicked off with a strong start, but turned the frustration up to maximum levels starting with the third level, the infamous Turbo Tunnel. While the stage starts out as another side-scrolling beat-'em-up experience similar the first level, almost immediately players find themselves dealing with an out of control speed bike in an autoscrolling nightmare of tricky jumps and dastardly dodges. It did have one thing going for it though: the awesome soundtrack. If you could feel the rhythm, you might have been able to reach the goal. Steve Watts at 1UP has a look back at music games that aren't exactly music games and posits that players needed the music in order to have a chance in hell at finishing the stage.
Once you fought your way to Turbo Tunnel, you found a reason to invest in controller manufacturer stock. This stage put you on the back of a zooming speeder and threw a seemingly endless supply of walls at your 'toad -- and we considered this "fun!" But the headache was soothed somewhat by noticing that the game set a tune to the beat of your approaching threats.
The rhythm element turned this stage from rote memorization to... okay, rote memorization with a beat. The level was sadistic no matter how you slice it, but it became significantly more manageable if you timed your movements to the song. The music didn't even kick in until you were already on the bike, and the two moved at a steady clip together.
The Turbo Tunnel was basically the end stage of Battletoads for a very long time when I was a kid, but eventually I memorized the sequence of obstacles and was able to move onward. I was able to make it through the frozen ice stage, the surfing challenge, the snake pit, and more all the way up to the long vertical shaft packed with hazards. That became the new end of Battletoads and, frankly, by that point that was just fine with me. If you've never experienced the horrors/joys of the Turbo Tunnel, check out this video of the stage in action. Pay attention to how the music meshes with the gameplay while trying to comprehend how Rare expected a majority of players to complete this within a reasonable amount of time.