Didn't even know there was a Reverse Knee? How is it normally executed? Is it present in Melee/PM?
Well, since no one answered... a reverse knee isn't actually doing a knee backwards, but it's a phrase used to refer to when the knee sends your opponent opposite the direction Falcon is facing. For an example, go to 1:33 here, where Scar reverse knees the Marth after his up+b:
If you are good at spacing knees, it's good for edgeguarding and also killing people earlier in combos [where in Minus your knee would always have to go in the direction you're facing, in Melee/PM you can space to make it send them backwards].