I remember a space RP where people got the choice to create a race for their character. Similar to how people in a fantasy may be able to choose elf, troll, etc. Anyways this RP started alright with some pretty colorful characters but the problems started to arise when certain people started interacting.

One person in particular created a feminist, Nazi race that instigated fights, and attempted to take over the plot of the story. The problem with it all was that we were that far into the RP that booting her out would essentially break the storyline.

It wasn't necessarily overpowered when you look at the charactersheet, but the problem was that there were so many loopholes that were utilised that it became overpowered without realising.