Just a blurb in the rulebook under carriers to the effect of:
"weapon blows with a carrier that matches the PC race or Monster Type listed on your monster or character card will effect you for the damage called. This overrules any other carrier immunities on your card."
Example: Bob the NPC is playing a Goblinoid with "immune to normal and silver weapon attacks" on his card.
Sasha the Fighter runs up (but stops outside charging distance) and hits Bob for "5 Normal" with her sword. Bob calls "no effect"
Sasha drops the sword and pulls out a silvered axe and hits Bob for "5 silver." Bob says "No Effect" again.
Squinting in the poor light, Sasha sees that the creature she attacked appears to be some sort of green humanoid. She drops the axe and pulls out a hammer (observers begin to wonder how she manages to run) and hits Bob for "5 High Orc." Bob rolls his eyes and says "No Effect," frustrated that he is unable to land a hit on Sasha even as she seems to be doing her level best to drown him in weapon reps.
Getting frustrated, Sasha puts down the hammer and pulls out a dagger and hits Bob for "5 Goblinoid." Bob shrieks in pain.
Jimbo the rogue, amused at the goings-on, but realizing they need to finish this fight pulls his bow and hits Bob with a "50 Magic Assassinate."
BOB EXPLODES!! (did I mention he was a grenadier with funky immunities? No? Sorry.)
Sasha is blown in half by the explosion and goes to resurrect. Jimbo takes the copper from the goblin, as well as Sasha's coin pouch.
Jimbo buys Sasha a drink with her own money while spinning a yarn about the 20 other goblins he had to kill, preventing him from rendering First Aid,
Jimbo is a jerk.
Wow... that kinda got away from me.