I didn't put multiclassing rules in the Black Book because it's only five levels right now, and I wanted to keep things simple, but we've actually been using them almost from the start in the Age of Worms playtest campaign.
Or rather Melissa has.
She started out Sumia as an elf rogue, but during the first adventure (The Whispering Cairn) they ended up killing an owlbear mother (though they didn't know it at the time and were understandably more focused on trying to not get collectively mauled by it).
Melissa wanted to keep its cub as a pet, and I told her that the next time she leveled she could take a level in ranger in order to pick up the Animal Companion talent (basically gain Medium or smaller beast of your level, levels up with you so it doesn't quickly become a wasted talent choice).
Since then she's mostly focused on ranger, snagging a level in wizard much more recently for a Sustain Darkvision talent so she could see in the dark while sneaking about, and also not give away her position with a torch.
I just updated the Black Book with the first Appendix D document (for those of you that already bought it, just check the product page again), which in addition to multiclassing rules adds the cambion and tarchon races, the monk and ranger classes, and suggestions on things you can make with monster parts (as with the Black Book we want to know what you like/hate about it).
The gist of it is that when you want to multiclass, the next time you level up you choose another class. This is mostly how it worked in 3rd Edition Dungeons & Dragons, but since the numbers are lower and there isn't any assumed math-by-level you can organically develop your character without inadvertently crippling yourself.
You don't gain the new class's weapon or armor proficiencies, or its saving throw bonuses, because all of that is assumed to be stuff you learned prior to adventuring. We're waffling between having you spend a talent on weapon and armor proficiencies, or just letting you pick them up for free if you take the time to train in them. Probably end up doing the former.
Here's what you get by multiclassing into a new class:
- Cleric: Favor equal to your Wisdom, Lance of Faith, Rebuke Adversary, and a cleric Domain talent.
- Fighter: You get +1 to hit and damage with all weapons, but you can swap out +1 damage for another fighter talent.
- Monk: +1 to hit with unarmed strike, unarmed strike deals 1d6 damage, Ki equal to Wisdom, Flurry of Blows, and Fighting Style (might drop that though and require you to pick it up later because monk seems to get quite a bit)
- Ranger: +1 to hit with weapons, Great Outdoors, Hunter
- Rogue: You gain Sneak Attack and a rogue talent. Thinking of also adding a bonus skill to the mix.
- Wizard: You get Detect Magic, Magic Missile, 4 Mana and you choose a wizard talent.
Your WP and VP increase is based on what the class gets when it levels up, not what it gets at 1st-level. So, if you multiclass into fighter you get +4+Constitution WP and +2 VP, not the 6+Constitution WP and 4 VP a 1st-level fighter would normally starts with.
At 2nd-level and up you just get whatever the class normally gets. So if you start out as a wizard and multiclass into a rogue, you get Sneak Attack +1d6 and a rogue talent, and if you take another level in rogue you get a bonus skill and talent.
Related, Adam (Albright) is working on hybrid class rules, which will ideally let you do a spellsword type mix at 1st-level.
Dwarven Vault is our sixth 10+ Treasures volume. If you're interested in thirty dwarven magic items (including an eye that lets you shoot lasers) and nearly a dozen new bits of dungeon gear, check it out!
Just released our second adventure for A Sundered World, The Golden Spiral. If a snail-themed dungeon crawl is your oddly-specific thing, check it out!
By fan demand, we've mashed all of our 10+ Treasure volumes into one big magic item book, making it cheaper and more convenient to buy in print (which you can now do).