Funny you posted about this, I found out about it not too long ago (saw it the other day from downloading it on DC++), I then showed it to my friend yesturday when I went to his house.
I must admit that even though I am skilled with Mario 3, watching this video makes my jaw collapse in total awe, I mean, this makes me look like an amatuer Super Mario 3 gamer, and yet I can argue that there is no way in HELL that he could had done all of this in the one go. True, his score and lives remain, but I believe he musta done a lotta video trickery or stuff in order to make it appear he had kept his score and lives all the way, as if he did do this all at once.
And if you think about it, by watching closely, you can see that he risked hitting himself or risked losing his lives by merely showing off on those slow-scrolling ship and tank levels, and why should he even bother to? He didnt lose a life in the entire thing, and had 99 of them by the end of the video! The video clearly states it's a "time attack" clip, not a "show-off" one
Anyhow, none the less it is a must-see for all SMB 3 fans, so those who havent saw it yet, go now!