First lock down the camera on a tripod. Get one shot with Freddy standing there, one shot of just the background with the car driving past, and one clean shot of the background (called the background plate or back plate). Now you have all your elements.

Use the pen tool in Adobe After Effects to create a matte and patch the shots together. At the moment of desired impact, make a mask around Freddy and animate it so he rotates, like he’s getting hit and thrown out of frame. Apply motion blur or other effects if you’d like.

A similar effect could probably be accomplished frame-by-frame in Adobe Photoshop. But the AE route is much easier and more efficient.

Export your gun shot clip as a filmstrip file then import that into Photoshop. You’ll see the sequence frame-by-frame. I create a new layer over the filmstrip file and set the layer to “color burn.”

Then I just paint something that looks like a muzzle flash (to me, at least) over two consecutive frames. Sometimes I use the blur tool to further shape the muzzle flash.

Then save the filmstrip file and re-import it into Adobe Premiere, Final Cut Pro, Avid, Sony Vegas, or your NLE of choice.

Alternatively, you can create muzzle flashes in Adobe Premiere or After Effects by overlaying still images of muzzle flashes onto your video and then keying out the background.