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