Hey there! Anyone knows how i can duplicate frames of animation from a high poly character to its lower poly version?

Depends how its animated i guess
If your using a skeleton you should be able to take the animated skeleton and skin it to the low poly model
if your using vertex animation , then uhm.. as far as i know you are screwed
hell i found myself wondering how to copy keyframes from one object to another the other day, never did bother lookig into it, i knew i should of paid attention to animation instruction in school