I'm curious what you think battle personalities should entail. In my mind it wouldn't really be anything beyond a couple phrase barks characters shout out in combat, and I don't really see how that would contribute to world building. Though it would be good for characterizations, which I also fully support.
World Building? Game industry typically talk about Lore, World, Universe, Quests, Story, Characters,etc.
Narrator could help a ton with giving lore to a player, like she could tell stories about the world/lore. Lets say you're close to enter Druid's Grove, before that Narrator might have told some stuff about Druid's Grove to a player, so hes a bit aware. Or two Character in the party might have discussed about it earlier like Astarion and Gale. "Hey, have you been in Druid's Grove, I heard the chicks are hot, Nah, too big butts.
