Eyecraft's version seemed great until i recognised a lion-like face on a closer inspection. I'm still tweaking it over and over, but i've realized that you either had the breeding mask thing and leave out the chin or put the chin and leave the mask part of, which is bad aswell. The trick is to show a bit of both, but so far I've yet to realize how.

The Emperor's Pride Chapter knew they could get the edge they needed over the Xeno's by splicing the might of the king of the jungle's DNA into their marines.

A problem with adding darker shades to the chest was exactly another bug related problem: harder inbetweens make it look like a red beetle or a ladybug. Also keep in mind this sprite model is supposed to be recoloured according to other chapter patterns/colours, so overshading might turn up to be a bit of a risky choice for me :p.
It's not the "amount" of shading that makes something like that difficult. It's the number of colours you use to shade it. You don't need to add darker shades, you need to darken the darks and mid-darks you have.
On a closer inspection I've just realized I need to rearrange the hunchback aswell. and change it back from a ^ to a V perspective. The leg stance could use a tweak aswell- Is not as quite as good as I thought it was.
Nice work on that. Looks much more terminator-y now.

Still contrast issues. Working on a dark canvas is a trap. Your sprite's contrast should be able to stand up to the scrutiny of a lighter canvas. If it doesn't, retreating to a canvas that downplays the problem won't fix it. Black canvas or not, it's still to a large extent a saturated red blob to the eye, it's just that now the eye has lost the clear silhouette of it.
Still got a tonne of unnecessary colours. I don't see the contrast really fixable until the palette is controlled.