Gravity in sidescrolling areas

If the developers ever make an OSX beta 13 (grumble, grumble), I know this'll be the first thing I try to implement. But until then, maybe someone else wants a crack at it?

Here's what to do first:

* "Open air" combos are fully walkable, unlike in traditional methods.
* When Link is on an "open air" combo, his Y value is incremented by a certain amount (gradually increasing as he falls)
*...unless Link is just above an unwalkable combo, or a "ladder" combo.
* Pressing Up will change Link's direction but won't make him walk upward.
*...unless Link is on a "ladder" combo.

Ladder combos should also have the effect of locking Link's facing direction to up once he starts to climb. This would result in a more realistic decent animation.

Erm, is there a way to determine what specific type of combo is next to/under Link at the moment, _L_? If so, it seems like it shouldn't be that hard to make LA type sidescrolling areas.