The website says you can play the game with up to 4 people if you get a second core set. I don't see the rules in the book anywhere on how to do that though. Could someone help me out here? I'd appreciate it.

First, you can play with three or four players with only one core set. You may run out of tokens on occasion, but this is pretty rare. Two of the threat trackers can be substituted with pen and paper or ten sided dice, etc And, you won't have enough cards for four fifty card decks.

As far as rules go, everything is the same you just reveal three or four cards from the encounter deck each round.

yes, i ve always thought the extra core set something you would want to work up to for that amount of players. the game is perfectly playable with 1 core set as above. you just need paper for threat, some extra tokens.