Here is the full list of all 19 Divide By Sheep achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Get all stars in Dark World
Beat the Dark World
Burn the first sheep
Get all stars in Ice World
Beat the Ice World
Put a wolf in a cage
Get all stars in Green World
Beat the Green World
First blood
Eat the first sheep
Drown the first sheep
Get all stars in Spring World
Beat the Spring World
Get all the achievements
Use the totem to crush a critter
Send a sheep through a portal
Beat the 5th world
Beat the 5th world with 3 stars in all levels
Get all achievements in 5th world