Here is the full list of all 15 Brain Bait achievements.
Collect 5 Treasure Chests
Collect 25 Treasure Chests
Collect 100 Treasure Chests
Finish the First Floor
Achieve Two Stars For Each Level On Floor 1
Achieve Three Stars For Each Level On Floor 1
Finish the Second Floor
Achieve Two Stars For Each Level On Floor 2
Achieve Three Stars For Each Level On Floor 2
Finish the Third Floor
Achieve Two Stars For Each Level On Floor 3
Achieve Three Stars For Each Level On Floor 3
Kill 10 Zombies
Kill 50 Zombies
Kill 250 Zombies