Karlach can be saved in Baldur's Gate 3 by repairing the infernal engine in her chest, which is slowly killing her. To do this, players need to:
- Have Karlach as a companion.
- Find 2x Infernal Iron located in places like the Blighted Village and Zhentarim Hideout.
- Take Karlach and the Infernal Iron to Dammon, the Infernal Mechanic (a Tiefling blacksmith) in Act 1 (The Hollow), Act 2 (Last Light Inn Horse Stables), or Act 3 (Forge of the Nine).
- Dammon will repair her infernal engine, preventing it from overheating and destroying her.
Even after repairing the engine, Karlach must eventually return to Avernus to avoid burning up. Different endings allow her survival, including going to Avernus with Wyll, the player if romanced, or both. Another ending involves turning Karlach into a Mind Flayer, which frees her from the engine but changes her fundamentally. A unique, more complex way to save Karlach involves playing as her, romancing Gale, and following a questline that allows her to become immortal with a new divine heart, but this is a challenging path. In summary, while the infernal engine can be repaired to save Karlach from immediate death, her ultimate survival generally involves story choices leading to her return to Avernus or transformation into a Mind Flayer. The game currently does not allow a simple permanent cure without narrative consequences.
