I liked the result so far. I know it's still a work in progress, but I noticed a few points:
0:10 I saw that you're aiming for cohesion in the graphics (which I think is great), but then it would be necessary to change that life bar, because it has many color tones and the Mega Drive couldn't produce graphics like that.
From what I could see in the video, you're using an image for the life bar and altering its X scale, correct? You could generate that image with 4 tones and red and use dithering to create smoother transitions between the colors, so it would be closer to the style.
0:14 I don't know how much you want to replicate the original game, but the RunJumpAttack isn't controllable in that way - once you executed it, you couldn't control it in the air. Since it's a high-damage attack, I suggest it shouldn't be controllable either.

0:31 It doesn't make sense for the enemy to get up just to lose their head (literally). This should happen automatically on the last hit, without the enemy falling to the ground.
0:35 I would remove this "wait," as the screen didn't even move 50px before another pause. This slows down the flow of combat too much, hindering the sense of progression in the game. In the original, this pause happens in this place, but there are 2 differences:
1 - The first fight happens without the player moving the screen.
2 - Since the resolution is 4:3, you have a sense of progression between pauses.
Knowing how to balance the space between pauses completely alters the rhythm of the game.
1:10 You can see the enemy's shadow "leaking" outside the bridge. A simple way to avoid this is to place a fglayer there, recreating only that part of the scenery - although this can cause problems in the final battle, when someone falls near the bridge.
Another simpler solution would be to shorten the shadow. It would still leak, but much less.
Oh, and I think it would be worthwhile for you to separate the layer with the water and the island in the background into different layers (you could even use the "Water" effect on the water sprite). This would help with the sense of depth in the level
