Now, I'm not one to be picking on little glitches... But stabbing yourself in the foot every time you try to stab that darned snake gets old really quickly after you realize "Hey, I'm doing damage to myself even when there's no enemies around! Look, a snake! Uhm... How do I kill it without killing myself?"
OK, I got the red symbols attack mechs and blue symbols attack spirits... But how the heck do you figure out which towers attack ground and which towers attack air?!