Here is the full list of all 15 Invasion: Brain Craving achievements.
Recruited Clarissa.
Defeated 10 Unholy Dead!
Defeated your first Unholy Dead!
Enter Post-Apocalyptia
Recruited Doc Brown. Now if only we could go back in time!
Recruited Aisha.
Recruited Peach. She was in this castle all along, hero.
Recruited Jeth.
Recruited Blue. Ga-ry, Ga-ry, Ga-ry!
Recruited Red. .... ..... ....... ....
Defeated 50 Unholy Dead!
Defeated 100 Unholy Dead!
Defeated 150 Unholy Dead!
Awoooo! Awoooo! Defeated the Werecar miniboss.
Rerolled your game!