Thank you
@PrincessLego for making this thread. I have done this a few times before and REALLY regretted it in the end. I find that I am the type of person who would, if I was a simple enough character, go along with anything (being mind-controlled, enslaved, turned into an animal, WIPED FROM EXISTANCE OR KILLED (YES THIS HAS HAPPENED BEFORE), etc.). I have realized that there are a few rules in an RP that can keep Mary Stues and Anti-Stues out of your RP.
Rule 1: To keep players from becoming too OP, make a rule so that everyone has to sign in COMPLETELY before you can begin RP. If someone disobeys that rule they should be asked to re-sign in or be kicked from the RP and kicked or banned from your plot.
Rule 2: Take care to thoroughly read through the characters backstory and their skills, weaknesses, etc. Some people will try to say, "I have no weaknesses" or "I have secret powers" or simply "I don't know". If anyone in your RP tries to do those, politely ask them to come up with something, have their weaknesses and strengths chosen for them, or leave the RP. Again, if the rules are disobeyed, don't be hesitant to remove that person from your RP and plot.
Rule 3: Encourage your RPers to be polite and/or open to others. I have learned from an unfortunate experience where I over-reacted to this, that some people will do something that humors themselves and/or annoys and angers the other RPers, causing the previously wonderful experience terrible for everyone. If you can't find out who did/said something mean in your RP, delete the RP and remove all players from your trust list (/p untrust or /p untrust all should work but I'm not entirely sure. If that doesn't work, do /p remove (username) going through your trustlist to remove them all). You can restart your RP later and re-add the people you trust.
Rule 4: This goes only for the creator of the RP. NEVER add anyone to your RP/plot before they know EXACTLY what your RP is. Make sure you know what the backstory of your RP is before you create one or even consider creating an RP. ask around for ideas if you need to, or you can just go to someone else's RP if you feel uncomfortable managing an RP. If you have ANY doubts about starting an RP, DON'T DO IT! Trust me, If you're not sure about your RP or you're not comfortable with adding/trusting people you may not know to your plot, you probably shouldn't start an RP.
I hope this helps!