Oh Hey thanks for playing it!
Yeah, current "level system" was made and tuned last minute, 2nd level introduces the "Slugman" which is the second type of enemy, and from level 3+, it just decreases the drop chance of "power orbs" and increases the rate that these "Slugmans" appear..
I will however continue to work on it, perhaps introduce a few more enemies, and hopefully have a proper "level system"
Thanks for your feedback!