I like this idea a lot for multiplayer. At least for mma the turn frames are so small and it’s easy to forget what you were doing just a few turns before. Being able to watch your ghost replay what got you to the present would really highlight the good or bad aesthetic of your movement. It would also feedback tactical information to help you decide what to do next.
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This might be a better idea if you could hit a key to show a replay ghost just for one ghost cycle (Ctrl + B).