Here is the full list of all 14 Tower Ball - there are Incremental Tower Defense achievements.
Build 100 bomb towers
Shrink 10,000 Balls
Shrink 100 Balls
Shrink 1,000,000 Balls
Shrink 50,000,000 Balls
Shrink 100,000,000 Balls.. Maybe take a break?
Spend 1,000,000 gems.
Build 100 gun towers
Build 100 electric towers
Build 100 shrink ray towers
Build 100 acid towers
Build 100 magnet towers
Build 100 saw towers