When I was in VA everyone played smash so I kinda just lost interest.
AT's? I say Glid Tossing, Platform Cancelling, JC Item toss, Z Catching (when items are thrown at you), B reversing. That's pretty much it Marth doesn't really have a lot of AT's that aren't universal besides the Stun Jacket.
One of the major milestones I had was learning the Mk Mu, not because of difficulty but through lack of MU exp. It took me a while to get it actually haha (early 09)
Plateaus for me lately have been a lot lf trivial things that most people may not consider a big deal. For example not whiffing moves, at first glance it seems easy to just not do it once figured out. But I view things a bit more on a scientific level if you will. I need to know everything about why something does or does not work, I also test through things over and over to make sure I can apply my findings.
The biggest problem for me was learning to be patient. Up until Mlg DC you can look at all of my vids and they could easily be compared to the way Leon, and Ramin play. At MLG DC I learned that that kinda playstyle can only bring LIMITED SUCCESS. The reason is because of the constant dashing and foxtrotting.
It's really bad to do despite popular belief, it has its uses but not as often as they depict it to. What I mean is that you are able to be punished when dashing or foxtrotting BEFORE you can shield. At higher end competition that style will lost more times than not.
For example take Neo (founder of that style) while he's very intelligent his success was always capped because of his playstyle. Sure he beat a lot of good players, but higher up he often would not (see ADHD, Ally, Havok, Dehf, Meep) just to name a few.
Now on to a style that is capable of unlimited progress, You've probably guessed it... MikeHAZE's playstyle. Walking and shielding only on reaction is an amazing thing. You will never be caught off guard and you'll ALWAYS be able to react and counter act any situation.
If you want a real example take my performance in singles for MLG DC I got 33rd needless to say that is ****ing horrible in my eyes. After being eliminated from Singles I knew exactly what the issue was(my playstyle which is the same as Neo, Ramin, Leon, Minty and Anaky's). So the rest of the day I did nothing but break all of those previous spacing and approaching habits that came with that playstyle and I did everything I could to refine it to a similar fashion of how Mike plays.
Needless to say I got 4th in Doubles afterwards the next day beating some really amazing players.
Finally the additional steps I take to improve are constantly playing perfecting my craft, learning the ins and outs of other characters frame data (to gind out the best punish given the situation), having a notebook with analytical MU descriptions mainly on how to cripple each character, and trying to say on top of who's beating who and improving and looking at vids.
That's pretty much it