Title. All of the mundane damage (which sadly only can come from the bolt) is doubled for the shot. Now please understand this before talking about crossbow balance (Though the mundane damage on other items not working is pretty lame and needs to be fixed)
You can't get any mundane damage added to your crossbow attacks from either skills or the crossbow itself, only bolts.
I'm not sure if I want crossbows to be buffed. Throwing weapons gain damage from , so they only become strong later. Bolts, however, tend to have strong spell and status effects that make them powerful early on. This gives mages who don't have strong melee a way to get through early game. I don't like how bolts work with Tinkering though. It's kind of annoying to have to hoard until you get the last skill, and even then those bolts don't scale very well on the last few floors. Scaling them up, however, could make things a bit too easy for players by giving more space to diversify instead of having to focus on spell power to get through late game.
It's not about them being buffed. It's about the fact that crossbows cannot add any mundane damage types (not that it isn't there on core game crossbows, but that it literally is brought down to 0), and critical hits with crossbows double mundane damage. On bolts you'll get a few points of it at most, and thus your critical hits add awesome +5 or +6 points. Yay, I guess, only people who use crossbows a lot have the right to feel cheated there. If anything, I think it would be cool if crossbows could get mundane damage bonuses but the source of such damage were encrusts (with even one recipe being a 0-craft one). But that is just me.
Does this mean that the 12 piercing damage from the "Diggle Ring of Digglish Torment" is not added to any crossbow shots?
Oh ok. What is mundane then? I was assuming that you meant the types blocked by Armour Absorption but now I have no idea.
Yes, types blocked by Armour Absorption. Meaning "crushing", "slashing", and "blasting". Piercing is not blocked by AA (because it's "piercing"), and is thus exotic.
Ah yes, my bad. I just get confused because it seems like a "physical" type of damage and therefore not "exotic".
Which is why it is "mundane" and not "physical". Don't worry, most people do that mistaken assumption on the beginning (it took me 7 characters until I noticed, myself).
Now I have this weird idea where Tourists are resistant to mundane damage, but receive more exotic damage. "Oh, look honey! That lich is about to give us cursed flesh boils of a thousand years! Quick, get the camera!"