Fixing the Entire Super Mario 64 Source Code [video]

That's a lot of dedication, remaking the game for N64 hardware to speed it up.

I wonder why they didn't write it as standard x85 (or ARM) software.

Especially given that they have to fight with the compiler to have it not do certain optimizations, and use per file compilation flags.

That was quite interesting. I learned a lot just by watching that, and it was an incredible improvement at the same time. It just shows that you can greatly improve something if you really set your mind to it.