my last comment was to report that an enemy in king's games just give us negative gold. They were fighters from 43~48 levels. I believe this is the problem but i'm not sure.
Bug detected! I had more than 1 billion money, but after a battle in the king's games, it turned negative! please, fix this! It's a print to comprove the problem: http://prntscr.com/3vklun
I am just thinking about a new special misson. Howabout a mission that you are the bloons, start with some money and gets more money when your bloons reach the end of the map and each bloon have its cost. After each 15 bloon types a new wave starts, so you get some money and the enemy monkeys can put new monkeys on the map. And the objective is to make the enemy lose 150-500 lives!!!
 "Flies"){kind=icon}
 "Battle Sails"){kind=icon}
 "Swords and Souls"){kind=icon}
 "Crusaders of the Lost Idols"){kind=icon}
 "Thrones of Fantasy"){kind=icon}
 "Crystal Story II"){kind=icon}
 "Idle Mine"){kind=icon}
 "Dragon Pals"){kind=icon}
 "Desktop Tower Defense 1.5"){kind=icon}
 "Clan Wars 2 - Red Reign"){kind=icon}
 "Adventure of a Lifetime"){kind=icon}
 "Esgrima 2"){kind=icon}
 "Bloons TD 5"){kind=icon}
 "Planet Juicer"){kind=icon}
 "Waterfalls 3 - Level Pack"){kind=icon}
 "This is the Only Level"){kind=icon}
 "This is the Only Level 3"){kind=icon}
 "Epic War 5"){kind=icon}
 "New Star Soccer"){kind=icon}
=D