Needs some balancing. At Pabulum Pit, which appears to be the highest level zone you still only get 1 or 2 exp and gold per kill, despite the monsters being more difficult than early maps. I recommend increasing the rate at which maps become more difficult, and have gold and exp increase based on the difficulty of the map. Great game, and I can't wait to see what updates you're going to be adding!
The exponential growth of both monster difficulty and money output should be higher. At higher levels I have to increase by hundreds of waves before I finally reach one that is challenging enough.
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Thanks! ;)