Here is the full list of all 13 Cows VS Vikings achievements.
Disable your first cow
Disable 25 cows by archers
Disable 25 cows by wizards
Disable 25 cows with artillery
Disable 25 cows by freezers
Build 4 kinds of towers in a single battle
Disable 200 ninja cows
Earn 5 barrels of milky Milk
Use Thor's Hammer succesfully for 50 times
Upgrade 15 towers in a single battle
Put out the same burning tower 10 times
Put out 50 burning towers
Sell 40 towers