Larian Studios Forums Baldur's Gate III Baldur's Gate III - Story & Character Discussion Lae'zel Act 3 romance - SPOILER

Actually, you dont convince Karlach to become a Mind Flayer, even if Orpheus volunteers or you start considering it, Karlack explains that it might be the only way she can live. So by allowing Karlack to turn into a Mind flayer she lives because her heart stops being explosive. Karlach is really happy about the choice in the end.