I've played around with making shapes transform into other shapes with Flash,
and a friend suggested that I use After Effects instead.
I have learned rotation, fading, and moving position,
so that leaves the transform.
Is there something like the shape tween in Flash?
An easy way to transform a square into a triangle lets say.
You can animate mask and shape layer paths by moving their vertices around which could include copy&pasting different shapes at different times, put there is per se no automated shape tween. So if e.g. you start out with a circle mask and enable the animation and then paste a triangle mask from another layer, AE would interpolate them, but the result would for all intents and purposes be different from what you can do in Flash. Generally, though, it's the kind of thing where we are approaching the "nobody would do it this way in AE" point. It's just as much a matter of the overall workflow - since the result will always be pixels, it really doesn't matter how you create an animation and people will use multiple effects/ layers, some of which could be driven by masks of course. Many times it is more practical to create complex shapes this way rather than ending up with tons of keyframed masks....