I don’t know if any game series has a higher ratio of difficulty to simplicity as the Monkey Ball titles. Just use the analog joystick to tilt a 3D landscape to use physics and gravity to steer a plastic ball containing a money into a goal tape. But within that simple premise is some of the most devilishly hard gaming of all.
Especially in the original game, Super Monkey Ball. (Okay, the original original was Monkey Ball, but that was only released in Japanese arcades, and is pretty similar to the arcade mode of Super anyway.) To truly beat S.M.B. you have to complete 50 stages of Expert, then the secret 10 stages of Expert Extra which only appear if you finish Expert without using a continue. This means doing it in three lives, plus whatever additionals you can scratch together by collecting 100 bananas, while completing levels like this:

It isn’t the focus of this post, but here’s a run through all of SMB1’s Expert, Expert Extra and Master stages. The thing about Super Monkey Ball is it’s very hard, but it looks even harder. Check out this utter insanity (34 minutes):
Being separated into discrete levels like this and being so exacting in execution, one might think that the incentive to cheat at this, by splicing together footage of different runs, would be high, but due to some interesting factors it’s not as easy to do this like one might
think. Goober13MD made a video (13 minutes) explaining why you can’t just edit together your best plays in Shotcut and present that as a world record run:
But that video is from eight years ago, and since then some people have, indeed, tried to cheat, and for quite some time succeeded at getting away with cheating at speedrunning this most ludicrous of games. Here’s GooberMD13’s exposĂ© from four years ago at uncovering a cheater (48 minutes):
And two years ago they put together this epic 1 hour-6 minute video about ancient records revealed to be the probable work of cheaters: