First things first... you need to consolidate your pallette.
You know you only have 15 colors to play with (excluding the mask color -[which incidentally should be index color 0, or the first color in each bank of 16 colors]) anyway, on some frames the count is up to 18, and the final frame 19! - So you need to be careful when making those edits... I'm not sure how you've managed to duplicate colors like this but you have... so be aware.
I've taken the liberty to convert your pallette to a decent range... and I've consolidated it across the sequence of frames for you. (In promotion theres a single palette feature across animations that maintains the pallette integrity from frame to frame making it easier to not screw up)
Your mask color is now in the correct place... (Color 0) and there's no duplicate colors... it's now easy to see where those extra colors were used. (when you cut and paste the head to 'animate' it)
May I point out what I feel is a major flaw in your graphic? Look at how many colors you're dedicating to the toes...? there's 6 colors there? That's a helluva lot of colors to be used on such a small surface area... where inversely you've used 4 colors of pinky/purple on the main body. I'd rethink this. Asthetically you'd be seeing more of the body than the toes, so dedicate more of you limited color pallette to making this less gritty... plus you've got two spare colors...
Now as far as animation's concerned you've been told what by your programmer? there's only 30 blocks of 32x32 pixels per enemy... riiight....
This is how you should try and visualise your graphics when it comes to storing them and your own personal limits. In terms of a Megadrive/genesis they store Graphic data in chunks of memory of 256x256 pixels at a time. This is then split into characters of 8x8 pixels, and each character then has an associated pallette register chosen from 16 banks of 16 colors each. But you know this already don't you? It's been a while for me to be honest and I can't recall how banks of these 256x256 pixels a Megadrive has in memory at any one time, I know it's more than 1... but might be around 4... I'm not sure... you'll have to check with your coder. We used to dedicate banks to various aspects of the screen, so 1 bank would be for the Backgrounds, another would be for Sprites, Another would be for the Fonts and HUD and so on...
What I'm presenting to you here is a way for you to visualize memory physically in terms of how much you've got to play with. It may help you in the long run for the duratoin of the project.
Incidentally, your using 11 frames so far of the allocated amount. But there's a LOT of repeated characters so hopefully if your coder has a decent character stripping tool then you may get some frames to play with. Depends on his tools.
But that's by the by... first thing you need to sort is that pallette. I'd use less black too. And be aware that the background color is similar to some colors in the pallette - a good rule of thumb (to avoid messing up your masks) is to make color zero something garish that isn't a part of the color scheme of you sprite... I'd go fro bright green myself...
I've wittered enough... I'll leave you to it...