My understanding was that Tau let the hero fight and just tagged along and that in addition to his overly large ego annoyed me. I do agree that his descriptions were funny, though.
From what I understood, Ysabelle was poisoned, though it wasn’t made 100% clear if the Knights Coronet did so. They betrayed Luther and his men and opened fire on them during the Broken Spire siege, but that doesn’t mean that they poisoned Ysabelle. Though it definitely seems like they at least wanted her to die (because why betray yours allies otherwise?).
I guess I’m just salty about the not-resolved storyline which I hoped would happen. Tau has just a bad personality (so arrogant) and the fact that his storyline only gave slightly more insight on what the Knights Coronet are up to is weird. Like, Luther returned to cure Ysabelle, so… why are the traitors still allowed around? Surely he told Ysabelle what happened at Broken Spire. I do hope @Sirrian might explain at least that a bit more. I’m also unsure if Luther did end up staying in Sword’s Edge - he said he didn’t want to, but with the big update of Ysa and the other troops, it was said he started rebuilding there.