General spoilers below.
Astarion's Act 3 approval and disapproval is all over the place. Reasonably, this is to cover that he may or may not be partway through a redemption arc, without an easy split like DJ/Selunite Shadowheart. But it tries to account for two opposing playthroughs at the same time, and it's very janky. There are conversations where he approves of every option. There are conversations where he disapproves of every option. More importantly, it's not reactive, so you can have Vampire Ascendant Astarion approve of your evil PC feeding Yenna or claiming that your best quality is that you're kind to everyone, and you can have Spawn Astarion disapprove of helping Aylin against Lorroakan even though in his reactions he's sympathetic to Aylin and expresses delight in watching her wreck Lorroakan beforehand.
To fix this, I think his approval needs to be split into two routes upon entering Act 3: a good-ish path and an evil path, i.e. how he started out. He doesn't have a clear point of divergence like Shadowheart does, but I think this could be handled by adding a counter to some earlier decisions that weighs whether your player has been influencing him positively or negatively.
Araj and Yurgir would be the biggest contributors, alongside whether the PC let him bite in Act 1, but I think major quests should also have an impact; saving or raiding the Grove, saving Last Light versus Durge killing Isobel/Tav giving her to Marcus, saving or killing the Nightsong. Certain arc sidequests like Barcus and Mayrina might be worth adding in for a +1/-1, but the biggest hinge is how the PC treats Astarion, so you could have cases like a bad start redemption arc Durge where he still comes out 'good' in Act 3. However, the quest tally should weigh enough that if you have an evil PC who picks every evil option, even if they're nice to Astarion at every opportunity, he should still be on his evil approval set. That's how I'm envisioning this, anyway, though YMMV in implementation.
If the player breaks even on this count, he should default to his evil path. It may be a good idea to set the floor for his evil path above zero, so that the player has to be either significantly good or significantly nice to him to start seeing his character change in Act 3 (and if the player is unkind to him, then no matter what else, he won't change.)
Spawn ending automatically sets him to the good approval set and Ascendant automatically sets him to evil, if he was on a different track before.
From there... 'Good' Astarion is far from a nice person, and he'll still disapprove of handing out money on the streets or Lawful Stupid brand heroics. But at least his behavior could be made consistent, so that it's 'good' Astarion who approves of rescuing a random kid from a hag and 'bad' Astarion who wants you to sell off Nightsong.
I also think it would benefit to have this factor into his final decision at Cazador's Palace. I'm not saying I want getting the good ending to ever be easy. But I think it's tone-deaf that a goody-two-shoes Tav that's been romancing him sweetly for the entire game has the same DC on talking him down as an evil Tav who treated him as disposable. If you killed the Grove and told him to bite Araj? If you've confirmed all his beliefs that the world is a cruel place and power is the only way to thrive? You should be rolling those checks with disadvantage.
Hypothetically, though, that one should probably look at the number on the counter itself and not just whether he's in his Act 3 good/evil path. The Tav that did everything as cruelly as possible should have a harder time persuading him out of the Rite than a Tav who just ignored Astarion up until now, who shouldn't really have a different DC than a Tav who also ignored Astarion but saved the Grove and tipped him onto his good set of approvals.
But that part's less important than establishing some character consistency. Any thoughts?
