One aspect of a game that is never dwelled upon but is always appreciated is the allowance of artificial difficulty. This is basically the player making the game more difficult. This can involve things like trying to play through the game without using certain weapons or abilities. However when that isn't creative enough sometimes the mechanics of the game can be bent to create new challenges for the player.
In Super Mario 64 there are 1ups that can be found by climbing certain trees. Unlike 1ups found in boxes these tree 1ups follow Mario...everywhere. Basically the two guys in this vid trigger this special 1up and try to do the Red Coin challenge without allowing the 1up to get them. Aside from showing off some skilled playing the videos are hilarious and show off the incredible mechanics that made Mario 64 a game far ahead of its time back when it came out.
You've probably seen these videos before but if not you need to check them out here.