For those who haven't figured out how to play..

The linked post explains it well. Just break everything, buildings and all, and your "Deer Hell" level will increase. As the level goes up, bosses (animal police) will appear. (Hidden quests are completed by defeating these police officers). Each boss has its own patterns. For example, the polar bear only takes damage when its transformation wears off up close.. something like that. There are a lot of ads, so avoid them if you can. If you're going to play, be prepared to watch reward ads.