I found a bug. On level 23, if you send all your troops to the same planet as your opponent, they'll eliminate each other simultaneously and the level will just keep going with zero troops on either side.
It was kinda fun to see what happened..
How to load custom cars in the main game (not sandbox) for easy badges:
1. Open garage in main game.
2. Select "See all cars" from Kong sidebar. Load car of your choice. (I recommended Fertiger.)
3. If it says you don't have enough money, click "Load in Sandbox"
4. From Sandbox garage, go back to main menu.
5. Press "Play" and select level, and your expensive custom car should be in the garage. No payment needed.
Play as normal. Earn badges. :)
Which mac model ?