I love this game, it's honestly a lot of fun. It needs more content, but, otherwise it's simple and easy to play. For anyone looking, you can gain every hero and unit through the stages by grinding them. Yes, this includes legendaries and epics (including heroes you encounter). Drop chances are low, but increase at higher stages. You do not need to spend anything to get ahead in this game, currently top 8%, I plan on spending after this simply to support the devs. They have a great game.