halcyon thorn
I was thinking after the beast is defeated and goes up to the ceiling what if he crashes down and makes a hole in the floor then the players fall into an even older part of the dungeon (lava floor or something) or maybe where lore or something pops up. (Who created dungeon)
I will say I haven’t caught up with all the lore so I don’t know if thats already mentioned or explained 
rose basin
halcyon onyx