Multiclassing: it wears me out just thinking about all the twists this can cause for game mechanics, play balance, and immersion. Even in the early editions of Dungeons & Dragons there was a process for acquiring multiple classes. Older versions of the game have pretty brutal restrictions on multiclassing. You’d have to be a certain race to access classes, only certain class combinations were allowed, you’d suffer XP penalties, you’d need very high core attributes, you could only ever switch once (and you couldn’t switch back!), etc. I’ve already started tackling the issue of multiclassing with Prestige Classes in an earlier post, and I suppose the mere existence of Prestige Classes suggests a pretty free-form multiclassing system. Still, it’s worth thinking about again to make sure I’m happy with the way it’ll work and to make sure I consider the potential for abuse in multiclassing before I start really designing the various classes and races.
I remember when I first started reading the rules for d&d 3e, and pretige classes were introduced into the game. There had been special classes you had to “qualify” for before, but nothing quite so modular and free-form. I remember a friend of mine and I sitting down and realizing that the prestige classes were a great opportunity to flesh out our own campaign. As the campaign progressed, each player’s character discovered some kind of organization or style that lead to the creation of entirely custom prestige classes for each one, and truth be told it felt epic.