This is wavedashing (when they make the smoke and move immediately. Used often for edgehogging.)
You jump and immediately air dodge diagonally towards the ground. Depending on how heavy a character you are the longer or shorter the wavedash will be. The floatier you are the longer u wavedash. Luigi had the longest wavedash in Melee.
ToonFlaresin: you are talking about L-canceling which is another AT(advanced Technique)
For info on ATs check out
Smash Boards, probably sounds like a bunch of bs to you guys so I suppose one could classify me as a geek.