Common problem players and how to deal with them
Problem Player: The player who insists their PC is the only canon PC and all the other players characters are "non-canonical OCs"
Solution: Declare their PC non-canon. This will, in their mind, render the entire game non-canon, allowing them enjoy the game again as a non-canon AU where the other PCs exist.
Problem Player: The player who keeps powerscaling your setting and insisting the goblins are "haxx-based low diff mutliversal" or some shit.
Solution: Just use your chain-scaling outerversal massively FTL smurfing to solo stomp 10/10 the argument
Problem Player: The player who never shows up, and none of you remember meeting, and when you search their social media you just get images of your own death.
Solution: Leave a message carved into the bones of an unburied heretic beneath the new moon asking them if they're still around and, if there's still no reply, you may need to find a new player.
Problem Player: The player from an 80s PSA who thinks they're here to pledge themselves to Satan and is clearly disappointed this is a roleplaying thing.
Solution: Sadly, this is just a find a different game group thing. Luckily, there's plenty of Old School Revival games that apply modern game design to the old-school satanic recruitment style that you can recommend them.
Problem Player: Jock who doesn't care about this nerd shit and is just here to impress their nerd crush.
Solution: This one is just a waiting game - by act three, they'll realise that they actually love RPGs in a big emotional climax. Make sure to have the game involve heavy-handed symbolism for the jock's personal problems to speed up the narrative.
Problem Player: Inhuman creature who's wearing the skin of one of the game group and is clearly planning to devour you all.
Solution: Don't be racist! This thing came from the Andromeda galaxy to hang out with you, the least you can do is let it play our human games and give it some snacks.
Problem Player: Sheldon Cooper