Here is the full list of all 15 Invasion: Brain Craving achievements.
Recruited Red. .... ..... ....... ....
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 Clarissa.
Recruited Peach. She was in this castle all along, hero.
Recruited Jeth.
Recruited Blue. Ga-ry, Ga-ry, Ga-ry!
Defeated 50 Unholy Dead!
Defeated 100 Unholy Dead!
Defeated 150 Unholy Dead!
Awoooo! Awoooo! Defeated the Werecar miniboss.
Rerolled your game!