HEROEs!
On Reddit users sks_innawoods Zathrus1 keeto has the adventure book and give some news
- new monsters
- new magic items
- Sunless Citadel has tons of characters
- Sunless Citadel is about 25 pages in length
- Sunless Citadel is at least 4 hours of play
So I found this. from dndnext