I have 500 layers, all that will end at different positions forming an object. Their first keyframes can be random, don’t need to move very far but each object needs to land in it’s final position. Is there an expression I can tie all of these layers to that will randomize all of their first positions but allow their final keyframes to be specific?
You need to apply it to every layer indeed. Since you want all layers to act differently, it wouldn’t make sense to parent them to say a null, and randomize that.
Expressions only affect the value of the parameter they’re applied to.