I must just suck, cause I can never Uair as an approach. It never connects and leaves me wide open.
I also cannot up air into knee. It seems that the up air lasts just too long for me to react with a knee. They are always able to get away, even in training mode. :/ Any help, cause I am really frustrated.
Well I can help you with the second part through text at least. Take a look in the two videos I have. See how I wait just a hair of a second before doing the uair? If you want to combo into the knee, you
need to do the uair fairly close to Falcon. There is plenty of hitstun to do this. Just watch where they're going, and if you feel like they're in range for the uair but it'll send them to far for the knee, just do a second/third uair instead. That's still a solid 32-38 percent damage combo. Also, you can't go from uair into the knee above a certain percent. They simply get launched too far.
As for approaching with the uair, it's really all about timing. Practice doing shorthops and then pulling out the uair about a half second before Falcon lands. You know that white blur that appears when you do your uair (shows the hit area)? You know you're doing your falling uairs right when only the very first part (where Falcon's feet are in front of him) is visible. Also you do have to get pretty darn close to do it, which is why I recommend baiting out smashes or other punishable things with dash dancing or any other similar technique, and then short hopping into your falling uair while they are recovering from the lag. This is also good if you expect your opponent to air dodge into the ground on their way back to the stage or after a jump. Basically what I'm saying is, don't approach with your uairs a whole lot. Use them sparingly, allow your opponent to make mistakes while keeping just outside their range, and then set them up with it when you see your chance.
Empty shorthops, that is just short hopping and fast falling without doing anything, is a good way to confuse your opponent and keep them guessing as to what you're gonna do. You see good Greninja players do this all the time. Using this technique will make your uair approaches safer since your opponent won't know whether to attack, shield, or dodge when you shorthop towards them, as they'll always have to guess whether it's just more mindgaming or an actual attack.
As a final note, I
highly recommend that in just about every circumstance that you mash out your jab right after whiffing a falling uair. Falcon's uair is tied for the lowest landing lag of all aerials in the entire game. 9/10 times you'll be able to stuff their shield grab or punish their spot dodge with a swift Gentleman. If you whiff and they rolled behind you, just do an ftilt at them. If they rolled away or you whiffed at a distance, quickly get airborn again or maybe even roll if you think they're going for a grab or shield if they go for the dash attack. Sometimes you'll get punished for it by extremely fast characters being played by good players with fast reaction times, but most of the time Falcon still has the advantage after the uair.
