Halsin is a companion and potential love interest in Baldur's Gate 3's campaign. The First Druid of the Emerald Grove, you'll find Halsin trapped in the Goblin Camp during Act 1. Making the choice between Halsin's freedom and Minthara's order to massacre the druids is part of the main quest.
Baldur's Gate 3: How To Get Halsin To Join Your Party
Recruiting Halsin to your party as an active member is only possible in Act 2 of Baldur's Gate 3. Here is a guide on how to make that happen.
