Thanks for your suggestions. I made the game for fun and to learn how to program a GB game in C. When I made the game, back in August, I had free time, now I'm a little bit bussy. However, I want to eventually make some cartridges, so I will definitely try to make some corrections before I do so. 

1. Iirc, the first monster is the only one that makes random moves, and yes, it's possible that sometimes it gets stuck in a particular area  of the screen. I'll change that. 

2. Yes, that's something I wanted to do when I had time. The way it works right now is that the more sprites on screen at the same time, the less smooth their movements are. That's because they don't move at the same time (in the code, that is), so making them go in smoother movements would slow down the game. It's done like this because when I started programming, I didn't think I would end up making a game. It can be corrected, but I need to find some time because it's not something quick to do.

3. Well, I like it like this. Perhaps, I can add an option to make the sprite bigger by pressing select or something, so everyone who plays the game can choose between two or three sizes.

Thanks again for you feedback!