The obvious problem with this game is that you weren't able to implement the shop.
This would have been fine, but there are a few things that make it really annoying. The first being that coins don't mean anything, and worse than that. They actively hinder the gameplay. I suspect they are physics objects that collide with the player and that's why you get slower when collecting them. But the real issue is that if you jump into a coin from below, you instantly fall back down. In some situations this issue had me stuck in a hole of coins for like 30 seconds without a chance of escape, while being shot at by enemies.
The second one is how you use the merchant instead. It functions as a story teller in the final game, this would probably have been a great use of the sprite, but the monologues he gives almost always break the fourth wall and just drive home the point that the game isn't finished.
I think you could have just made the best out of what you got, lets say you pay the merchant some coins and then he gives you a little bit of story. This wouldn't have been a massive time investment and would have made the game feel a lot more complete.
Another area where I feel like the game is lacking is the world design. Most areas area completely empty aside from coin boxes, which are not really that good of a reason to go there because of the things I stated above. Another thing that makes this even worse is that the entire map, including ability upgrades is visible from the start. At some point I just looked at the map to see where I needed to go next and skipped all the other optional rooms.
All of these things made the game feel way too big for what it was. When I reached the second map screen I was like "there is a second map ?"
And then after reaching the third one "Oh god there is a third one."
It really is unfortunate, because what good there is, is really good.
The transformations are really fun to find. They may be your metroidvania ability archetypes, but they were really well implemented and felt good to control. The combat, while simple was very satisfying and the enemy designs too were fantastic. Especially the horse riding boss that throws three projectiles at you.
The whole aesthetic was fantastic. Very reminiscent of traditional Japanese art.
Don't take this to heart though. It is very hard finishing a game of this scale. I would know, I have failed multiple times during the years. And the fact you have made this is amazing in itself.
Keep it up guys.