Alright, I like the abilities to rip youtube in a format that will work in windows media player, so instead I'll present my information here
Metaknight can abuse this stage with no room for punishing, pure and simple.
http://www.youtube.com/watch?v=CKVaYbC1SuE
Notice how with he can activate the invincibility cape while still in invincibility frames, allowing him to move from edge to edge with no punishment what so ever. Now, the first reaction you might get is "Stalling is banned" Forget stalling, this can be abused for offensive purpose as well, letting Metaknight force his way to whatever part of the stage he wants. Then there is his B cancel on his side B, also making him unpunishable. Yes, he can do that on Battelfield too, but in no way to the same extent. Then as you can also see, he can cancel his up b right into a down smahs, which thanks to his cape will be easily set up as he moves underneath you. This stage allows Metaknight to surpass perhaps his only weakness, his lack of aerial maneuverability by giving him the ability to move flautlessly through the stage, with 0 opportunity of being punished.
Gameplay example:
http://www.youtube.com/watch?v=p0nc8l0XKEY
G Money is a power ranked player. At the time, Red was a next to no one. This was a very early tourney for him.
One thing to note first, the bubble at 3:33. Coming out of the bubble, Metaknight is not as vulnerable as every other character thanks to his down smash and up b.
Generally, you'd imagine the lava would fix stalling, but not with Metaknight. Thanks to his side b and multi-jumps, he can camp off the stage, then side b flawlessly onto the edge. The stalling opportunities for Metaknight here are simply too great. At 6:44 you can also see him attempting to do the same with the horizontal lava, while actually failing at aiming for the edge, but that was a player mistake, and a player mistake should not factor into stages being legal or not.
an poor example of offense Metaknight abuse the stage
http://www.youtube.com/watch?v=DbLTzmnxvno
this stage has been banned for a long time, so finding tournament matches to showcase the troubles on this stage is hard.