Many people complain about the difficulty of the game curve is too high, or zombies supply too little.
Some players buy and unlock all skills, and they told me that the gold useless.
So version 1.6 Improved it -- you can buy zombies in the battle.
The Pack Store will open every 5 levels, there are 3 purchase options, including zombies and level up items. Of cause it also depends on whether you unlock them.
The purchase price will increase with difficulty, but I believe you will buy them.
In addition, I modified the background music, but this does not make much senseːsteammockingː