...yeah, so i get the impression that what i want to do is well beyond me.
logically, i think i'm making some sense of it. i need to make a shader perform multiple passes on the same mesh. if i want N after images, N passes need to be made. each pass would need a world position of the player at that point (stored in a buffer), and it would also need the mesh positions of every part of the player (also in a buffer, although probably a more complicated buffer). so something outside of the shader, like a C++ script, would need to maintain these buffers and execute the passes.
unfortunately, it's hard enough as it is trying to find UE4 custom shader knowledge. the documentation is incredibly obtuse to a beginner, and the one excellent video i've found can't go further than "make your own custom shader block in the material editor." which is still a necessary step i suppose, but barely scratches the surface of all of the problems i'm trying to solve. i even switched up to UE5 today, which has quickly reduced all of the relevant, more complicated public resources to zero.
also, happy day 100 of the streak. i would really like to include more images of stuff i'm making some time, but again, there's just nothing visually interesting about learning new engines or writing down story in a document. hopefully soon.