as the lvls progress you shuold make them give them more gold because they do get more health and make them do more damage and give the town more health or add a heal button which tou have to pay to use
hey how about a lvl 10 ? with like 20 free treasure boxes and like i unno a boss wave with like your own special ability and maybe like bonus lvl like take over the other castle?:P
if your a noob you should start as a death knight and then chaos archer than the wiz because wiz is really hard and its only good when you know what your doing