Ok so in order to get this achievement I would go to a custom game, if nobody else like a friend will help you.
So choose solo, and custom game:
Map and Mode:
Mode; Hunt,
Map;any map that will allow you to have a second monster.
(I chose the Fusion Plant)
Map Effect: Second Monster
So from there you want to eat as many creature as possible, I suggest not evolving because the second monster will attract the hunters,and when you evolve you lose your armour. So you eat as much as you can until your armour is full and fight. The second monster will distract other hunters witch allows you to pick one hunter at a time making the damage mostly going to the other monsters. So for each hunter you kill, eat them to regain your armour, and before you know it you got the achievement.