When you swap out a companion (or hireling) that character is unusable for the rest of the game.
What choices would you make and when?
That's the tough part. If I had to do this challenge, I suppose I would start by making Tav a draconic sorcerer, white dragon. 17 Cha, 16 Dex, 14 Con, 10 Wis, dump Str, dump Int. Hag's hair, dual wielder, ability increase (Cha). I'd pick the third feat based on how I was feeling. Maybe Alert, maybe elemental adept or spell sniper.
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Then I make a hard decision. Instead of swapping out characters to get Wyll or Karlach's storyline material, I just don't pick them up. I lose the infernal rapier, unfortunately, but challenge rules are challenge rules. And I don't want to lose the other characters by swapping them out.
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So, of the four left, I have to get down to three. i think I'm ignoring Gale. Again, I hate to do it, but rules.
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Shadowheart stays Trickery because I want to stay narrative consistent. I will use the respec to change her stats.
12 Str
14 Dex
16 Con
8 Int
16 Wis
8 Cha
Feats: ability increase (Wis x2), Alert
She'll end up using Luminous Armor and radiant gear.
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Lae'zel will go Battlemaster.
16 Str
16 Dex
14 Con
8 Int
12 Wis
8 Cha
Feats: ability increase (Str x2), gwm, alert
Special: potion of everlasting vigour
Fighting style: great weapon fighting
heavy armor, two handed weapon
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I respec Astarion into a Bard, which will subsequently take the swords subclass. There's something about the bard that fits Astarion better than the rogue, at least to me. I imagine him playing sad and haunting music on his violin. And there are bard spells that feel thematically appropriate to a vampire, in my estimation. Normally, for example, I wouldn't bother taking Speak with Animals, but in this case, i would. It feels right that a vampire would be able to speak with beasts. I'd also take Dissonant Whispers, Sleep, and in general, keep my spell selection to things I imagine a dark vampire might be able to do.
8 Str
16 Dex
14 Con
8 int
12 Wis
16 Cha
Feats: ability increase (Dex x2), ability increase (Cha)
Fighting style: two weapon fighting
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I can't really list all the gear I'd use as it would change somewhat throughout the game.