Reducing the frame rate of a single clip... how to?

I'm trying to create a video-game like effect of one video on top of another video of "real world".

I've got all the effects in place except one: How do I reduce the framerate of one clip inside a project?

I hope to find a native solution, although a plugin is acceptable if there's no other way to achieve it.

Do you mean you want to speed up the clip? You can use retiming to do that.

Thanks, but no, speed-up and slow-down is no problem.

I want to make it look choppy and old. Something like 4 frames per second, without changing the speed of the action. Basically I want to make it look like it was rotoscoped 25 years ago, but without having to draw every frame

I'd create this effect in another program like After Effects and reimport the clip back to Final Cut afterwards.

Like old film. There should be a couple or few in the free templates section of this forum. Can be created in Motion as an effect quite easily.

Motion... after effects... I'm sure that could work.

Are there no native solutions to do this in final cut pro X?