I don't remember if these are in the gallery, but still worth checking:
Pucca (bad end). To get her you need to take a loan at the Bank and don't pay. Lose the battle for a bad end pic.
Mouth Fiend. On the Brothel, hire a girl, and fail the charisma check (by being rough with them). Eventually the Butt Madame will kick you out. Look around the town and you'll get an encounter.
Note: this is like sort of an alternative path game. I never completed it because I got bored to death (sorry, not my thing), but has lots of pics, and apparently an alternative "game over".
Lord of Mount Xiuh: the main goal for now. Just keep going and look for one of the farthest mountains. It has a "normal" pic, and a couple more.
Also, I think the ghost has a bad end pic, not really sure.
And Urka (Orc) has a an animation aside of his extra "normal one", win or lose you should see it (just get intimate with her).