From Gimpyfish:
If down starts a glide, how do you fastfall?Gliding is really unorthodox, I think we just didn't try it enough because it’s so different. It’s also awkward to activate a glide. You actually press DOWN to start gliding with pit/Metaknight. Seems like it would be a great way to recover, but it might be pretty easy to edge guard. But we really don't know, it wasn't researched very much.