I recently watched the Simpsons Treehouse of Horror episode in which they did a parody of "The Island of Dr Moreau" and thought a mad scientist trying to turn people into animals could make for a fun minor character in my campaign. My players are en route to a dungeon and should be there in a few sessions, I'm thinking of making the dungeon the lab of a mad scientist who has gotten locked out of the lower levels due to a containment breach.
The details I have so far is that he is a gnome, currently named Prof. Moreau, who has created mongrelfolk while trying to turn a human into an animal.
The mongrelfolk are safely contained in the lower levels and have started to create their own society, I think the boss of the dungeon should be a Gibbering Mouther called One, as in Attempt One.
I think the Mongrelfolk should worship one as their leader and hate Moreau for keeping them locked in the lab.
What I'm stuck on now is what life is like for the mongrelfolk, what they believe and how they have organised society.
Make them live in terrible conditions, and look like monsters at first glance. This way your players will react to them as standard dungeons & dragons monsters, by which I mean kill them all. Afterwards, they find council chambers, crude medical facilities, nurseries, etc that imply that their society was surprisingly egalitarian and had a budding democratic government.
Give just enough of a hint beforehand so that they could have resolved things peacefully if they had been paying attention.
If harming your players emotionally is the goal.
I love this so much