I’m going to stick with Dungeons and Dragons (3.5 and the Pathfinder spinoff, not 4e), mostly because this is the only rpg I’ve played where splatbooks came into play often. For those who haven’t heard the term splatbook (it’s pretty common, but apparently not quite as prevalent as I thought), I’m talking about any book that isn’t part of the three core rulebooks. I’m sure some parts of this will relate well to other games, but I know some parts really won’t either. So take that as you will.

There seems to be a prevalent idea that if you can find a rule, class, variant, feat, or anything else in a splatbook, you can use it in a campaign being run by another GM. Usually brought up by the dark side of rules lawyers, this entitlement almost always comes from people who believe it’s their right to break the power curve of any campaign they play in. Sometimes, it also comes from players who just want to be cool, but these players are usually much easier to work with and can be very easily negotiated with to hit their concept while giving them a good amount of power but not breaking the entire campaign world.

There are many problems with this train of thought though. The first is that I, the GM, don’t always have access to the splatbook while planning a campaign. Many GMs tailor challenges for the PCs, not because they demand a particular solution, but to make sure they know of a solution that can be used while still keeping the game challenging. This is usually my approach, though I also throw in some arbitrarily powerful npcs intended for the endgame. Usually, if a PC comes up with an unusual solution, it’s good fun, but if a PC has an obscure power that solves everything that’s been planned for, it gets boring fast. I can’t plan for this when I don’t have the splatbook while making campaign plans, and most people only bring the splats to a session, they don’t leave them with the GM. Being willing to let your GM review the splatbook and hold onto it might help with this, but it’s still only a first step.

Something else I consider when allowing various rules from splats into play is the power level. I also don’t allow splats themselves, but rather approve every item from a splat on an individual basis, whether it be a class, feat, spell, or anything else. I try to use a core spellcaster as the top power level of any campaign I run. So, if you’re playing spellcaster, I’m far less likely to allow things from splats than I am for the melee classes that need some help catching up in versatility. That doesn’t mean spellcasters can’t have nice things though. There are plenty of noncore things that are cool, and even seem powerful, but really aren’t, and these can come into play easily. Divine metamagic and persist spell comes to mind as something that will never see the light of day in a campaign I run. Makes the cleric way more powerful than it already is, and it’s already one of the most powerful classes in the game. On the other hand, scintillating sphere is just a lightning based fireball, and easily allowable. Sure, it might up the power a little, but it doesn’t do so in any appreciable way. Everything is looked at case by case, and a judgment call is made.

Whenever I allow something from a splat, I always make sure a player knows that if it turns out that it can be abused in a way that makes them too powerful (i.e. more powerful than a core spellcaster), I reserve the right to ask them to rebuild, though I will do what I can to help them keep the feel of their character.

The thing about allowing any and all splatbooks is that new rules often combine in weird ways to allow really crazy things to happen. Consider the orb of energy reduced metamagic or ubercharger builds that can deal 10,000+ damage a hit. Pre-epic. No, you can’t do that in my game. One-shotting everything isn’t an rpg, it’s an action game. Even death spells allow a saving throw, and those are limited by castings per day. Low level death spells allow two saving throws, or a touch attack and a save. Death spells also have options that allow you to become immune to them So, seeing how this can happen, it’s always best to check the rules you allow into the game, instead of just saying anything goes.

Now, reading this, you might think I’m a horrible person who doesn’t want my players to have fun. This is actually not the case. First, there’s lots of fun to be had playing by the core rules. Second, I actually do end up allowing a lot of things from splats into my campaigns. It’s just up to my players to go over what they would like to do with me and let me review it so I know they won’t be doing something that doesn’t fit with the world (though in 99% of cases the world can be adapted), and more importantly so I can see it won’t break the game. I’ve had players happily playing Crusaders from the Book of Nine Swords, Dwarven Paragon Legendary Leader Mystic Fighters (only one of those classes is core), and Spellfire Wielders from the Forgotten Realms, among others.

The point of all this is you should make sure your players know that you’ll be reviewing anything they bring in from outside core. This is so you have an idea of what’s coming into your games and can make the game more fun for everyone, as well as make sure nothing obscenely powerful comes in to break your game. D&D balance will never be perfect, or even all that good, but you can make sure it doesn’t become worse. In essence, treat all splatbook ideas as potential house rules, and then allow the good ones into your games as desired by you and your players. It makes the experience a lot better for everyone involved.