I would say the swampmonster is more like... mild typical hentai at best. The monster is even humanized to a degree, and is basically the same thing as that swampbender guy in the show turned into a pervert. If I had to give an example of an option that could be turned on earlier, it would be bestiality, which basically presents itself in book 3 with the quest involving Appa, but could also have presented itself in book 1 via some sort of incident that resulted from losing or running away and hiding while Katara tags along to a mooselion hunt(hypothetical scenario, you can't run away from the hunt, and she's only present in one of the fights, namely against the dreamstealer).