Board Thread:R2D - General Discussion/@comment-26310078-20150423222321

The ability to buy zombie levels. For 50+ cash or so you can give your zombie +2 damage, health, speed, etc. Everytime you buy a level for a zombie +50/+100 dollars is added, so the next time you try to buy zombie upgrades its $50-$100 more expensive. You can level a zombie up 5 times. So assuming each zombie does 8 damage, upgarde the damage 5 times and the zombie will do 18 damage.  