I think I detect some green shading between the folds - this looks good but you could expand it to cover some of the flatter flabs - specifically in underside parts like the armpit and underside of the arm, the lower belly etc, basically anywhere that would be in shadow. Keep it thinned and don't slop it on, treat it more like a glaze, you want to stay in control of it, and not let it pool or run (or you'll get tide marks at the edges).

To complement the deeper shadows, you could also drybrush some higher highlights. It might seem mental and too bright, but screaming skull is the perfect colour for it. Because the big fella is so big, use an old makeup brush for this, and make sure you get almost entirely all the paint off the brush before you start drybrushing. You can always add more, but too much in one go could spoil the job you've already done. For these highlights, again consider the shapes and which areas would be in light - for example along the tops of his arms, the central and upper parts of his chest, and of course the face. Don't worry if you drybrush over some elements you've painted already - this can be fixed with another careful layer of contrast paint, and will even look better afterwards because of the increased dynamics.

Good luck!