You’re at the outset of your campaign, establishing starting conditions for your players – Attributes, Starting Level, Alignment Restrictions. You know what guidelines you need to have in place for your campaign. Your story’s success is paramount. Having addressed Alignments, now you may consider restricting the availability of certain Classes or Prestige Classes (P-C’s).
As with Alignments in the last CaSE post, restrictions or prohibitions should not come from your desire to be a tyrant of a DM or to set boundaries for every single aspect of character creation in an orgy of micromanagement.
There are legitimate reasons why you would not want certain Classes or P-C’s in your campaign. When these reasons stand the Players’ test of logic and sensibility, you will not be seen as a heavy-handed DM out to spoil anyone’s fun. Your decisions in this regard might even be helpful if they prevent a player from wasting time building a character whose purpose will never be achieved.
Some good reasons ?
A Class or P-C doesn’t fit the theme or setting of the story. A pirate, desert warrior, undead hunter, or wizard, might simply not work in a campaign that features no seafaring aspects, no deserts, no undead, or severely limited magic. A Cavalier might find herself out of place in a completely dungeon-crawling adventure where there’s barely room for the party, let alone a heavy war-horse.
A Class or P-C doesn’t exist in your campaign. Red Wizards of Thay, samurai and ronin, Nightsong affiliates, and other notably realm-specific Prestige Classes might not be present in any form in your world. Or the creatures for which the P-C exists to fight, such as Giants or undead, may not be common enough to warrant a Gnome Giant-Slayer or an Undead Stalker in the party.
A Class or P-C will be disruptive. Allowing an Assassin or a Blackguard in a party of otherwise Good characters might turn the party against itself. The mindless rage of the Frenzied Berserker, while useful in combat, quickly goes wrong when the supply of enemies runs out but the Berserker’s frenzy does not.
A Class or P-C comes from an unfamiliar source. Some Classes or P-C that players may want to play might come from sourcebooks / magazines / websites that you have never read; sourcebooks the group does not have; or from fan sites, tertiary sources or even from older versions of the game (v.3.0 in the case of D&D v.3.5). These Classes or P-C’s, because unfamiliar to the DM or constructed outside of canon, may have unbalancing effects on your game. The effects may be immediately obvious or, worse, might sneak up on your game later.
Alignment restrictions may pre-emptively prohibit certain Classes or P-Cs. If you decided to restrict certain alignments from the party, this may have had a carry-over effect that now restricts Classes or P-C’s. This would be the sensible outcome to the alignments decision, and probably fits your intentions. But having broadly prohibited Chaotic alignments for example, this might now block players from Classes or P-C’s for which ‘Chaotic Alignment’ was a prerequisite. Be aware of this side-effect.
Of course, as DM you can also ease access to certain Classes or P-Cs by relaxing, altering, or removing listed prerequisites. This might include dropping the requirement to take the almost-worthless “Alertness” Feat in order to access a Prestige Class; or to set aside required actions, memberships, or rituals to attain a P-C. But don’t be too generous and benevolent. Many ‘stock’ requirements of Classes or P-C’s are there for a reason. Your good intentions could pave a road to the Nine Hells for your story.
And if the players really want to play a certain Class or take on a dubious Prestige Class ? This is where you should consider this question, if you have not already :
What would be the down side of having that Class or Prestige Class present in your campaign ?
What’s the worst that could happen if you did allow the Class or P-C ? If you have solid reasons and can defend the decision at least against your own objective scrutiny, then it is easy to make the case to the player(s) to justify why the Class or P-C is not allowed.
But if you struggle to come up with a sensible explanation –or if your decision is based on personal tastes or biases– then you need to decide why you’ve made an issue of this Class or Prestige Class and if it really should be officially excluded.