Monster Classes?

[sambouchah]

I've seen quite a few monster classes in various books and online sources and things and I don't quite understand how to make them while keeping them balanced. Could someone explain it to me please?

Thank you in advance, Sam

[The Viscount]

I'm no expert on making your own monster classes, but the general idea is that the vast amount of special abilities gained is balanced by the fact that not every level grants a hit die. In the case of some monster classes, no HD at all are gained, and as such a character slows or entirely loses BA, save, hp, and skill progression in exchange for monster abilities. As for balance, it's a very difficult thing. Vampire, for example, is extremely powerful, but I doubt it'd be easy to play with the vampire savage progression (https://www.wizards.com/default.asp?x=dnd/sp/20030824a). Powers or no powers, having 2HD when facing a CR10 encounter is going to make life difficult.
Some monster classes are simply not worth it. The ghoul/ghast monster progression, for example, is 8 levels long and gives 4HD, whereas the gravetouched ghoul template is only LA +2 and gives the same things except fr stench, which wasn't that great.

[Urpriest]

Depends on the type you're talking about. The official ones (the ones in Savage Species and on the WotC site) are just the normal monster spread out over its ECL. There aren't any explicit guidelines on constructing those, just try to keep it roughly matched with normal classes along the progression, with more powerful abilities coming later, and compare to the existing examples for balance.

There are also some homebrew monster classes on this forum that work differently. Rather than reproducing the monster, they make a new class with a number of levels equal to the monster's CR, and build it like an actual class, with class abilities rather than ability boosts and no LA. That thread has some guidelines for making them, but again it's going to be a matter of comparing to existing examples.