Anybody know how this guy made this?

https://www.youtube.com/watch?v=GwPLSrwhehc

The only technique I know of doing something like this is by masking, but there's just no way he could've done this entire thing by masking right? I mean he would have had to mask every single frame by frame of every character in this video. I just find that very hard to believe. Especially considering how perfect it looks, is there some type of program, app or anything that makes this possible without having to mask every thing frame by frame?!!

He uses masking yeah. and Chroma keying. The intro scene with the Swordfish wasn't so hard since it already had a blue screen around it. All he had to do is use a blue chroma key on it, and mask out the rest of the remaining tiny bits

The running scenes look masked out too. So yeah, i'm pretty sure he spend quite some time masking every frame. Luckily anime movement doesn't use as many frames, and it seems most sequences he mapped out are the same case

Still, very nicely done. It is indeed time consuming