There is a VIP version of the game available on in the store that costs only $1. Despite what they tell you in their app page, everything the VIP version of the game is available in the free game. The difference is you don't have to watch a 30 second ad in order to gain those things, you just get them instantly when you hit the button. I feel it is well worth the $1 price tag as those ads are quite tiresome after watching the same ones over and over!

For your convenience, I'll list what it says on their app page:

  1. 10% Additional medal reward when returning
    Instead of the option to watch an add or continue without the 10% bonus, you just have a button to continue with the 10% bonus.
  2. 20 free crystals from time to time during the game
    I just recently found out that this is also in the free version, you just need to play an ad to gain them just like in Endless Frontier.
  3. A large amount of gold gifts every 10 minutes
  4. Every 20 minutes, 2 times the attack power and 2 times the battle speed
  5. Data sharing: Free version
    This means that you can play both of the versions with the same save.