the clip looks great, it's really coming together!
One thing that will help you I think it to actually change the format to widescreen. Keep the framing for the top and bottom part, but expand on the left and right. It will free you for the 2nd shot so that the demon doesn't have to be so close to the creature.
The first shot works well. Just thinking out loud, It could also be cool for the demon to swing both his arms for the hit, a bit of a delay between each arm (it's a double whammer kinda like Indiana Jones does in his movies). I'm mentioning it because visually the demon is so much smaller than the huge crab thing and that one punch is feeling a bit small. It's not a deal breaker but if you have time and energy, it could be good to make that punch a bit more powerful.
The impact of the punch is good though on the crab, not too slow nor too fast. Are those two long antennas able to bend for some overlapping action or are they stiff?
The demon in the first shot looks good, minus the punching part, which could get beefed up, but I would tweak sections of the 2nd shot first (about that later) before that aspect of the first shot.
As I mentioned before, I think the wider framing will help you. Right now with both creatures hugging the frames it feels a bit claustrophobic and story telling wise I don't think it's needed to have that caged in feel.
The 2nd shot definitely needs a wider framing and that notion gets triggered by the demon yelling at the crab guy at the end. On the first yell the head is overlapping the crab a little bit and overall the leg pose stays pretty much the same after the last steps and he feels more like he's just standing there and yelling. I think the pose could be more dynamic, mostly in the lower body section. The arms and the head action work, but maybe the screen right leg could be further screen right or he yells at the guy and the takes a step or two, kinda like gorillas after a big fight. Not that he has to pound his chest but something like that.
One thing that stands out is the neck snapping of the crab guy. It happens over two frames and makes it feel very snappy (no pun intended). I would give it another frame and then a few frames of softening for the settle. It's a big creature and even though we are breaking the neck/head part, it should still retain some weight. The rest of the creature feels nice. If could make the head dangle a bit looser, that would be even better, like it's really broken and just barely holding together.
The demon in the 2nd shot has a very slow first step. You could get away with the foot rising that slowly but on the way down it should be faster for a more powerful plant, as if he's steadying himself for the last grab and attack.
When he snaps the crab's head I would have the hand/arm movements be more separate from the upper body/head. The arms can start the movement and then 2 frames later the head follows. Right now that rotation is happening all over the body at the same time (x156 and on). So instead of having everything stop at x158 (after slowing down the snap a bit it could end at x160 or 161) the head would continue for a few frames as overlap.
And then as mentioned the end yelling could be a bit more powerful stance wise.
You're really far along though and it's looking very sweet!