You have to save girls in the city and during party talk with her saying that goblins are sex beast and later when she tells you to find someone to fuck them propose her to do it.
after I got those girls in the camp I chose the first option, saying goblins are good fuckers, priapra was blushing in text dialogue, then what do I do I do next? do I then suggest she fucks goblins the next day on wakeup?
EDIT: ok I managed to get it, I had to untick some tags that were fucking up the sequence of events.
EDIT2:heres the save from the beginning of the mini bad end.
1. first you talk to her(whitehaired lady)
2. then select the top option where it says goblins are good fuckers. then enjoy text ofc.
3. then go sleep
4. after go speak to her (shes on the big red chair in the eastern/right part of the house.)
5. select you should fuck the goblins(top option "why not you") enjoy text ofc.
6. then go outside and she will be on the top left/north western part of the map your currently in.
7. when sex scene ends go back in and talk to her.
8. theres two scenes that can play out depending on what your choice is, if you mock her or if you comfort her. the longer extended scene is comforting her. this completes her corruption. the other seems unfinished where shes chasing that high of her prostate getting poked.