edit: Wow, I left the reply window open for a while, came back to type up a response, and when I submitted it, there were a bunch of other replies ahead of me all of a sudden.
Not sure if I'm interpreting this correctly, but it sounds like you're asking how you can have a platform game character change to a special "edge wobble" animation when they are standing on the very edge of a drop-off, Sonic the Hedgehog style.
This can be done either with detector objects, or with the condition "is overlapping at offset".
You can have two objects that "hover" to either side of your character's feet, sitting just below ground level. If you walk over to an edge, one of the detector objects will no longer be overlapping the ground. You can use a condition to check for that and then switch to the edge wobble animation.
Is overlapping at offset
You can use the condition "is overlapping at offset", and specify an offset that would shift the character off the edge and slightly downward before checking for the overlap. If the the player is not overlapping any ground, then they are standing at the edge of a drop, and you can then switch to the edge wobble animation.
Hope this helps.