Ok, these animations were so cool! Really well done.
The game itself is really simple and seems very polished. But I get a feeling that it could be more difficult - like, on the slime level, he could shoot at the player position . As it was, I could simply go up and stay above the skull shooting bullets. Huh, you could also make so that the player can't get above the skull I guess.
One thing I noticed is that the difficult progression seems pretty off. The first two patterns are the hardest to beat (I will not count the final boss because). The slime level could be more challenging if not for the fact of the exploit I talked above.
All in all, a very nice game with clear inspirations on Undertale. The creator is man of culture, I see :P