Mechanithrall:
Skin looks pretty good. Try to work in some soft colours, to make it look like decayed skin. Some glazes of green, blue or purple. Look through Demi_Morgana's gallery if you want some dead flesh examples.
The grey armour on the front could use some deeper shading starting from the height of his chin and some stronger highlights on the shoulder parts. The highlight on his 'exhaust' is a bit abrupt. Smoothen the transition with some intermediate grey colours.
Metallic fists could use some more highlighting.
Grot base: Good work so far. Try to make it a bit more interesting and realistic by painting the wood.
Grot: Enough contrast on the skin! You could also work in some colours on this one. A reddish purple nose etc... Checkers on the sword is a good idea, but I would try to weather them. Like some paint has come off, scratches, dirt.
Metallics look a bit rushed. You should take you time on the sword as it's a prominent part of the mini. Highlight it more, use brown and black glazes for shading. Build it up slowly.
Keep up the good work!