Here you go:
You set the name of the character it should follow in the file.. If you don't change it (or you use a name that doesn't exist), it will just follow the first party-member.
I haven't tried it in pvp, but it works very well for instances - it will attack the persons target aswell if he's fighting against it.
Use Combat Bot with the plugin.
btw, it will also follow you if you jump down somewhere. I coded this because in many dungeons, people jump down some places to take a shortcut.