Here is the full list of all 9 Undead Overlord achievements.
Find a quick bite to eat at a Port-a-Potty
Whoa, you beat the alpha 1 skirmish mission! Is that possible?
Go back for second helping and finish eating the doctor in Mission 01: Born in a Small Town
Kill Barbara
Survive the counter-assault on the police station
Skewer 10 meatsacks with a zombie goat
Take out 5 meat-sacks in a single Tank Zombie stomp attack
Use a mind controlled meat-sack to kill another meat-sack
Burn through 2x chaos capacity in a single chaos rage burn