Explanation: this is a commentated, recent speedrun of Donkey Kong 64 which uses glitches and intimate knowledge of the underlying code to skip parts of the game and perform various time-saving tricks. It's a "tool-assisted run" (TAS), meaning the controller inputs are controlled by a computer script.
Heavily-commentated videos like these are fascinating because they explain all the glitches and tricks in great detail, allowing the viewer to appreciate what's going on.