The enemies are indeed coming from the sea! The enemies do spawn more every night but the increase isn't that big to notice in one or two nights so probably no one will ever notice while actually playing the game, but the system is there and can be tweaked to get better results. I'm glad you enjoyed the game and thanks a lot for the feedback. The different enemy types was something I had in mind but wasn't really possible to do in the limited time. I do plan on expanding the game so stick around if you wish.