It's easy enough in tile-based games where you try to estimate the fastest root based on a current cost and estimated remaining cost algorithm (a*). But 2d platforming just have me stumped. Well, almost. It's not too hard to make a pathfinder in which the computer players always jump in a pre-specified pattern, eg. max 4 blocks high, 1 block forward. Then it is possible to build a node map of the level which tells you exactly how you can move, and use a* on it.

But when you consider that you may have to jump down from cliffs, go backwards and land on a platform under the cliff it just falls apart.