Ok. So I had an idea for a pvp plugin. You make a large enclosed space for people to PVP in. It's only accessible by portal to stop people interfering in a pvp match, but passage through this portal is conditional. If there are more than x amount of people inside the enclosed space the portal goes to, you can't get in, the portal simply won't do anything for you. Basically it's a way to do private PVP matches in a way that stops trolls from interfering by throwing a TNT into the middle of you or something.
