Try pushing the shapes more, I made the shapes sharper cause you mentioned you want it to be more menacing, I think the colours you have are fine so I didn't change much but I did make the gold more dull cause it looked a bit too saturated for a serious character. Also, tried out different style if the sharper designs isn't what you are going for. I recommend just playing around with the shapes more. For the anatomy and proportions, you just need more references, use 3D models if needed.
thank you

