Started a second "good" playthrough (with Drow-LoreBard) a few hours ago, am still arrived at the "blighted village". Begin SPOILERS: Karlach is already Member of my "Crew" and cleared some things with Wyll at the Camp, Wyll also just met his "Patron" just before the recent "LongRest". All the Dialoges in the Camp around this very Point at the "Timeline" of Progress through the Game points toward a "default" romantic relation between KArlach an Wyll (propably for the Case, that the PC itself does not interested in any romantic relations toward any of the two)... from this "Perpective" regarding of possible KArlach-Endings, the choice to go to Avernus together with Wyll seems the "good" Ending-Option for KArlach in Larians narrative "Line of Sight"...So i have low expectations regarding her more "fiery, poignant" Ending, especially if the PC build up romantic relations to Karlach...
