Super Mario Tabarnak
At first I thought somebody made a WWJD level.
First, he wouldn't play this.
Second, may he show mercy on the poor soul of the one who would think of playing this without savestates.
(man, even Kaizo didn't make the bonus game a level preperation requirement)

I can't remember if I mentioned Enigmatic Mario.
I recall somebody taking like 6 youtube videos (an hour?) to finish one level with savestates.