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