Here is the full list of all 20 Unholy Heights achievements.
Fill every possible vacancy
Make room for a top tier Demi-Human
Let a top tier Abyssal darken your doorstep
Recruit a top tier Cheepy
Conjure a top tier Elemental into your building
Complete the main quest
Have a resident skip out on paying their rent
Sucker a top tier Undead into moving in
Domesticate a top tier Chimera
Invite a top tier Demon into your home
Add a fourth floor to your building
Have an unemployed resident find a new job
Add a third floor to your building
Witness a resident swearing to avenge the death of their child.
Add a second floor to your building
Witness the miracle of monster reproduction
Even love can bloom on the battlefield
Let none die under your watch
Evict none throughout your campaign
Defeat the legendary hero at the first opportunity