It's funny how entirely by accident, Charisma has become an extremely important stat in my campaign. For one thing, I use the Vornheim rules for when characters are asking for directions in a city, and that's all with Charisma. There's even been two times when the rolls were so bad, a PC was actually attacked for asking directions, which is always funny!
Anyway, a while back I asked readers to give me ideas for what a dead rat magic item could do. I got this comment:
It's exactly what I did, but I also added the ability to turn into a swarm of rats.
For fun and without thinking much about it, I decided to add a 1d4 of Charisma damage for every time the user turns back into human form, because having been a swarm of rats shouldn't be the best thing to keep one social and human-like. The user happens to be a Barbarian with a Charisma of 7. Without doing it on purpose, on a whim for a set-back on a magic item that was maybe a bit too good for a then-level one character, I actually limited the use of the item to a degree that seems about right. Torad the Barbarian won't be able to 'spam' this trick for sure. Cindy, Torad's player, also did a great job of playing all rat-like without even being told that's what she should do, she just went for it. Torad used the pillows on the bed of his rented tavern room to scratch and dig inside them to make himself a sort of rat nest. Cindy even went and said Torad would try to bite Rhovanor (The Elf Fighter/Wizard) when he reached his hand towards him. I think it was the first time ever I had to tell a player that they didn't need to play a drawback to that degree, normally you have to push players in that direction. I gave both players bonus XP for an awesome RP session that night.
As a funny side-note, Torad also slept with someone's wife and her cuckold later went after him with 4 buddies, all armed with longswords. Torad had to turn into a swarm of rats to escape and now some people are saying he could be a vampire. Since lately they mostly go out at night to fight Deep Ones in the sewers of the city (long story!) some people are starting to believe it! Not that I've warned the players of that... Also, an actual vampire has heard the rumors and moved to that tavern to see if he will find a buddy! Fun times...