Here's a Work in Progress shot of Gambit along with a finished shot. You can see where I sculpted, parts-swapped, and added extra stuff on him. This is customizing, taking existing parts and combining them to form a completely new character. The head came from a Marvel Legends Cannonball with Aves Fixit Sculpt hair/features, ML Nova body, Walmart exclusive Nick Fury coat and arms, ML Loki hands, and the lower legs from an original ML Gambit figure.
It takes a Dremel rotary tool to widen holes and drill new cavities for parts to fit in, X-acto knives, sandpaper, hairdryer to soften the plastic so the figures come apart, filing, super glue, sculpting compound, and of course paint. Painting takes a long time depending how intricate you want to get and Gambit here is extremely detailed. Drop by my site www.jincustom.com and check out my Guides and Tutorials if you want to learn how to make custom action figures of your favorite characters!