It a very short clip, so it's hard to see exactly everything that's going on.
As with most effects, there are a couple things going on at once, there's some 'time remapping' where the shots slows down. Also there's a little bit of the shot that gets over exposed, they probably transfer modes and/or masks to create that.
2 Shots, option+Shift drag the clip to the top track.
Apply color or brightness/contrast effect to offset the look of the clip.
then apply mask to the top clip, adjust the shape to reveal the image in background
Apply a time adjustment to the top clip or bottom clip or both.
all will create a different looks.
This is much better in After Effects or Motion, you can do Effects in FCP but you will get better results, faster in a motion graphics app.
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