Here is the full list of all 9 Grompula achievements.
Kill Brain Monger
Survive until wave 20 in The Lab
Survive until wave 50 in The Lab
Survive until wave 20 in Archipelago
Survive until wave 50 in Archipelago
Survive until wave 20 in Looper
Survive until wave 50 in Looper
Kill Brain Monger's Ghost