Needs a way to get gems, like one per level would be fair. that would mean that if 25 coins average per level, then the ratio of normal:rare chests would be 2.5:1 or 5:2.
I don't want this to be about grinding. I think this could be a lot better without striving for coins and xp. Also, there should be default maps, like a campaign.
 "Robot Dinosaurs That Shoot Beams When They Roar"){kind=icon}
 "Epic Battle Fantasy 2"){kind=icon}
 "No Time To Explain"){kind=icon}
 "Treadmillasaurus Rex"){kind=icon}
 "Sandbox Hero"){kind=icon}
 "Fixation"){kind=icon}
 "Epic Boss Fighter"){kind=icon}
 "Epic Combo!"){kind=icon}
 "Idleplex"){kind=icon}
 "Crush The Castle 2"){kind=icon}
 "Collapse It"){kind=icon}