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