The issue with Karlach is IMHO embedded in a general issue that D&D and other high fantasy settings have: if spells like "true ressurection" or even regular resurrection are a thing and are readily available, it's really hard to have any real stakes in a story, epsecially if they are personal stakes as in the case of Karlach.
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I also couldn't believe that her quest basically just ends after her second upgrade in Act 2 and there is no way to fix her engine or give her back her heart in Act 3. It feels like something is missing here.

You could design an entire questline on fixing her. Just invent that the engine thing was part of a contract with Zariel and that's why true ressurection doesn't work. Make it so that in order to fix her, you need to break the contract or find someone who would cast "wish" on your behalf.
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That was one ofn the truly disappointing aspects of the game.

Last edited by The Red Queen; 23/08/23 10:51 AM. Reason: Added spoiler tags