I am not
(hot rod paint)
but heres my two bits : I do this free hand w/an air brush and some times cut a few stencils , and looking at just the second cropped pic a few of the lines are sharp and some look soft so it could be a few stencils to get the main shapes then freehand it all in so that they are not all the same that's what I'd say . You can do such things w/just stencils and either way it is very time consuming.
I guess you could lift the stencil or dust the edges and get close to the same affect ...

Doing that big of a job I'd cut a few main shapes, lay all the shadow color with a mid size gun w/stencils ,then come back with my shadow color in an air brush & rough it all in ,then do my darker color to get the depth ,and then come back through with the light color to bring it back out. yep! ... that's how I'd do it, and I'd get paid very well for it

The purple out line is impressive that whole job has lots of time in it but I can't say much for the green "I wouldn't use that pinstriper again, he don't know how to roll ."

pretty soon they'll have some kind of super thin stickers you can stick on and just cut to get the skulls and I bet WallyWorld will sell it.

T L