While I appreciate no forced ads and nice graphics, the game is too hard and impossible to grind without pay2win. When stuck, only way to make money and unlock new characters is to replay past missions. You get 8 coin per mission and it costs 2 fuel. You get 1 fuel every 10 minutes. After calculation it takes 41 hours nonstop to make 1000 to unlock a new character. Also upgrading character need rework, should be % increase instead of just +1 or +2