(I originally posted this over at the True20 forums)
Having done magic and combat, the next big area to convert to True20 in a running campaign is the classes (and prestige classes).
This is really the trickiest bit - moving from very specific classes in d20 to the three generic True20 classes requires a lot of thought if you want to preserve your existing feel.
There are essentially three ways you can handle such a conversion. The easiest is simply to ‘grandfather’ in existing characters. New characters, when generated, are done up using the True20 classes, and that’s it. A popular variant is to preserve the existing characters but require that all new levels are taken in the True20 classes. This is especially handy for NPCs where you don’t really want to do nore work than really needed.
A second alternative is the total rebuild. This alternative is to rebuild the existing characters using the new classes and feats, trying to match the capabilities of the old character as closely as possible.
While these are both popular strategies (because of the low effort required), they don’t address the concerns of the world builder. The choice of classes is actually quite integral to many settings, and contribute heavily to the overall “look and feel”. In these situations, you want a conversion process that will retain the unique differences between existing classes while building on the underlying True20 mechanics. The rest of this post will concern itself with this third alternative.
The first step is to normalize the BAB and saves. You shouldn’t have to do anything here except redo the charts and eliminate the multiple attacks. Drop spells known/readied while you’re at it; with the new magic system they are no longer needed.
The next part is trimming the feats. The idea is to eliminate all the free feats and bonus feats, using the rationale that characters will receive a feat every level. Remember that we’re only doing classes here, so keep bonus racial feats.
Next, trim the class abilities that are feats in the True20 system. For example, Sneak Attack and Trackless Step can be translated directly into True20 feats; they should be dropped from class definitions.
Next take a good look at arcana. Spell-like and supernatural abilities often duplicate the effects of arcana, even if this is not instantly obvious from the wording. In most cases you’ll want to drop these abilities as the character can take a feat to learn the corresponding arcana.
At this point, you’re likely facing two scenarios. Some classes, like the standard fighter or wizard classes, will be featureless blobs. Others, like the monk or druid, will have a large number of unique abilities that have no direct analogue in True20. How can we reconcile this with our need to preserve flavour?
We have two paths open to us, and thankfully they can co-exist.
One option is to follow the example set by Blue Rose and adopt the idea of heroic paths (which in many ways are the evolution of Mongoose’s character concepts). Classes that have been stripped of everything unique can be reincarnated as a specific example of a generic class.
For example, the converted wizard can be a heroic path for the True20 adept. Pick two of the class skills as the starting skills at first level and come up with four likely feats; the obvious ones are Familiar, Imbue Item, and Power/Spell Training x2. You could give examples of specialist wizards by picking different starting spells or dropping one of the other feats to broaden the spell selection.
You don’t have to stop at first level, either; you can extrapolate feat selection all the way up to twentieth level if you are so inclined. That’s a great way to demonstrate to yourself or your players that you can build characters that are near enough to your existing possibilities.
The second option is to retain a small number of class abilities that emphasize the uniqueness of each class. In my own campaign, this is the option I’ve chosen; I have fourteen core classes that have extremely distinct roles and flavour, and they’re very deeply woven into the fabric of the campaign world.
From my own experience, I’ve retained class features for levels 1, 5, 10, 15, and 20. The first level feature is essential; otherwise there’s no real distinction between classes. I’ve chosen additional features every five levels to maintain the uniqueness of the roles. Since I am still using the standard feat progression, my classes will be slightly more powerful on average than characters built using the standard True20 roles. Luckily, the revised magic and combat systems, IMO, are a little harder to abuse than the d20 rules.
The most important bit of advice, should you also go down this route, is to make sure that any abilities you retain really are unique. If you don’t have enough abilities, or if the abilities you choose are too similar to each other or to existing feats, you’re better off shrinking the number of classes. You can always create heroic paths for classes you need to eliminate.
Ultimately, the number of classes you end up with is a function of how important class is to your campaign setting and how different your classes really are. Once you’ve gone down this route, you may surprised at how many class abilities don’t really do anything unique or interesting; there are hordes of prestige classes that just shift class abilities between existing classes or grant spells to non-spellcasters.
My conversion is still ongoing and under playtesting; I’ve eliminated all prestige classes at this point (roughly 30) and still have my 14 core classes. On the other hand, I expect to end up with close to 80 heroic paths; plenty of samples to fire the imaginations of my players and really provide flavour for the campaign world.
One final thought: fewer classes is better. If you can get away with the three True20 classes, do so - just provide three to six heroic paths for each.
