That was fun! The mechanics were a little confusing at first, but I discovered my way into them. The art is really interesting; I especially like the generated fog effect! The character design is charming.
Despite not being very Game Boy, the sounds and soundtrack are quite interesting! They make for a unique experience.
The combination of various flashing effects, including the bullets and the final boss, might warrant a flashing lights warning.
All-in-all, good work!