I did it by myself within a day, that's why I hadn't time to check any bugs.. it is not fully developed yet and i know it! since i wanted to add many features in it like leaderboard and types of pens and even particles or even new types of enemies! But i am indie developer and i have no time at all. However, thanks for your feedback! I am really excited you are interested in my game :) Soon, I will fix bugs and will add new features :) !