I was pleasantly surprised
I was surprised and impressed at this tutorial - it seems well written; easy to follow and the web address was great.
I appreciated the lack of music - I feel more folk should do the same rather than wasting megabytes on an entire song. Lets us listen to our own music or learn in silence, if that's more conducive for our own learning.
It seemed easy to follow along - I knew most of the features already, but even had I not, I'd have been able to follow along no problem.
I'd disagree with a few of the choices you make - I'd personally either use the transform tool (q) whilst holding down shift to keep the proportions, or type in a number into the transform box. Similarly, I disagree that limiting the onion skin to one previous frame made it any easier and I'd use F6 for making new frames. Though folk don't need to know the shortcuts immediately, it'd be worth mentioning them!
The main point, though, is that your system worked.
I'd suggest you tell folk how to tween the movieclips to move Mario across the screen or just have a ore motivational end frame, maybe telling folk that they can now use those techniques to carry on and make a movie...
Though the tutorial seems good, it lacks gravity when it's your only submission - if you had a sprite movie that you linked to, or maybe a short 10s example movie to inspire us and show that you know what you're talking about.
Regardless, this is one of the better submissions I've seen. Good work.