And here's this glitch taken to the max using a TAS (in which a program is used to enter frame-perfect controller inputs). Apparently, a second controller is used to enter arbitrary code into RAM. http://tasvideos.org/4961S.html I don't really understand it, but it really blows my mind what some people think of.
The progression isn't particularly mind blowing, though. Once somebody notices a buffer overflow / register pollution of some sort, you note which area of memory it's executing and then reverse engineer how to modify that memory to execute particular instructions. I would expect a community like HN would consider this par for the course. That said, what's impressive to me is the amount of time and energy individuals…
And agreed on speedrunners! It's not something I could ever do myself, but it's one of my favorite aspects of gaming.