Here's my first custom action figure: T.J. Combo from Killer Instinct
I used as base a Jakks Pacific WWE Backlash Bobby Lashley figure because that figure doesn't look like Lashley except for the face.
I started cutting the arms at the biceps to add articulations there with a pair of screws. Then I sanded the face to make it thinner and to take off the little beard.
Then I made the borders of the shirt and the shorts with epoxy clay and then painted the figure torso with acrylics.
Next step were the boots. They were black so I masked them with epoxy clay so I could paint them cyan, trying to keep the ankle articulations functional.
Then I made the hair based on pictures of the character and finally I made the boxing gloves covering the hands with epoxy clay and keeping the wrist articulations functional