Here is the full list of all 12 All Zombies Must Die! achievements.
Kill 500 Zombies in one level
Complete "Dev Card Hunt"
Complete "Return to the Military Base"
Complete ALL character quests
Fully upgrade a weapon with any status effect
Witness Luxo joining the group
Witness Brian joining the group
Kill a Mutant with your fists
Complete a base quest without taking any damage
Witness Rachel joining the group
Use your first Smart Bomb
Kill a Zombie