Here is the full list of all 20 Flockers achievements.
Kill 500 zombie sheep
Blow up 999 sheep.
Three star everything
Three star every level from the first theme.
Collect 30 golden fleeces
Complete every level (including bonus levels)
Find and unlock all the secret bonus levels
Collect 20 golden fleeces.
Three star 2 boss levels
Complete a user-created level.
Try out 10 different styles of sheep (blood included).
Save 100 sheep from fall damage by landing on something soft.
Get 20 punk sheep moshing together.
Look at what you’ve hurt.
Explode 2 sheep while they are in the air at the same time.
Complete any level with a customised sheep.
Get 20 sheep into the exit at once within 1 second.
Have 20 sheep jump at the same time.
Unlock a secret level.
Complete the first 3 levels.