KaeYoss said:The main rules is what you commonly use IYC. If you only use the three Core Rulebooks, then they're the main rules. If you also use the splat books all the time, they're main rules, too. If you play in Rokugan, The Domain of Dread, Faerûn, Krynn, whatever, then the respective Campaign Setting is also main rules. And all house rules you agree on beforehand (like: "we have LN Paladins here" before they make their charakters) are main rules.
Thanks for the answer.
What I find difficult are when new books are presented, be it from WotC or 3rd party.
Usually the DM is very up front about what he allows or does not allow in the game, but there are times when an ability or rule has been used from one of the newer "main" books, that the DM has not time to read fully, but a player has read it and decided would be a "cool" thing to do. During a case like that, the DM is usually forced to make an on the spot ruling, sometimes after the fact, if he feels the spell or ability is too powerful for the campaign.
Of course, the DM is not expected to be superhuman and know every in and out of every book that is used, but being a player, we tend to look for the little things that can make our character more powerful.
