I don't have much to say about this entry because it's so competently made. It looks great (I love the GameBoy palette contrasted with the blue-ish shadows and the orange highlights) and it moves very well. It sounds very crunchy too, which I liked a lot!
The Ys-like combat is interesting but sadly I never got the hang of it. Avoiding damage in the smaller rooms often felt impossible and it didn't help that many enemies attack the moment you enter the room, without giving you time to position yourself. I gave up near the end, in the room you enter by wall-jumping from the bottom to get instantly mugged by two crows (my nemesis!). I had to redo it many times and if I somehow survived those first few seconds, another crow would instantly kill me the moment I paid 50 gems to open the door. (And that was despite having the Cursed Sword!)
There were other such situations that felt unfair, like taking the Cockatrice Tail's back to the save point: if I messed up the jump, the enemy would stay dead and I would be stranded, forcing me to redo everything. Simply having a switch to hit to create a shortcut would have done the trick, I think.
Wall jumping felt a bit weird: it seemed to me the character was facing the wrong direction and the horizontal movement was disproportionate compared to a regular jump. But it was really the only ability that felt less than perfect, and it remained very serviceable.
I think what I liked most was uncovering the many secrets and finding the upgrade items and rings. The power progression is also very noticeable and enjoyable. It's a good thing there's a map and I used it near the end to find where I could use my new abilities.
Overall that's a great entry that could use a bit of balancing near the end to be really perfect. Good job! ;)