Your legs are completely stiff. And your hat doesn't turn in sync with the characters body, it stays there and recolors looking stiff as well. The viewers right hand on captain cold is very poorly done, it needs some more work, like transitioning on time with the rest of his body. It may be the .gif quality too, but there's 2 black lines that appear when he turns there's under his arms, there's also white pixels that appear above his gun. May I ask what your plan with him is? Are you coding him into mugen once you've finished spriting? If so what're your plans for in game implementing?
With some more practice, and time invested you could have a very nice concept here.