I read on the old forums that weaknesses weren't supported by the current game engine, and I thought, why not? I'm guessing the resistance set-up is probably quite simple, like dividing the enemy damage by 2. So, couldn't you simply have a new type of "resistance" say, -Heat, -Cold, -Physical, -Light, -Shadow, as opposed to normal Heat, Cold, Physical, Light, Shadow, and make it multiply the damage by 2? I still haven't gone into flash coding much, but all it would need extra is simply making the .5 into a variable with an if then preceding it checking if the first character is a - or not (I forget the line that does that, midseg or something) The - sign could even come after the name such as Heat- depending on how you check for which resistance is appropiate.
So, what I'm saying is, couldn't that be a simple way to create a weakness?