I have to say, the graphics and sound design are outstanding! You really captured that gameboy feel, and the little touches like the screen transitions only add to that feel. And you did this without using a game engine? Damn, that's masochistic! But impressive.
That being said, the gameplay leaves a lot to be desired. Movement is clunky (I guess you recreated that aspect of GB well huh), because the player collision shape is a CHONK. Barely fits in doorways. Like, lose some weight, miss witch. That wouldn't be so bad if not for the pushing puzzles. It's still not clear to me how exactly it is supposed to work. I thought it was something like sokoban, but it's not. You can push blocks halfway, but only sometimes, other times the blocks don't move at all no matter what you do. There is no tutorial to teach you the rules of the block-pushing, so we're left in the dark.
The combat is really flat. Light attack has no reason to be used ever, since it only deals 1 damage for 1 mana, while heavy attack deals 2 damage for 2 mana, not wasting an additional turn. Defend completely negates damage for 2 turns, so if you just spam defend->heavy attack over and over, you can win any fight without taking damage. This is really boring however, because you have to wait for your mana to slowly regenerate every 3 attacks, and enemies have 10+ HP. So it's a slog. You can cheese the mana regen phases by just using reveal at the enterance doorway of the room with the ghosts, so the door that spawns to block your escape keeps the ghosts away from you.
Potions don't help either. Mana potions are actually harmful, because gameplay-wise you want your mana to run out, because if you cast a heavy attack at 2 mana, the enemies don't get to retaliate.
Overall, the gameplay loop and especially the combat could use a heavy rework.
As a piece of art however, this truly could have been one of the GB games back in the day. It's gorgeous. <3
I wonder what you could have made if you had used a game engine?