In the Emerald Grove, you'll run into a Tiefling named Zevlor. Assuming that you've resolved the conflict between the Goblins and the Grove by siding with the Tieflings, then Zevlor will be mentioned next during Act 2 of Baldur's Gate 3, but where exactly is Zevlor? Where can the Tiefling be found?
Finding Zevlor In The Mind Flayer Colony
At the top of Moonrise Towers, you'll face Ketheric Thorm. Defeat Thorm's first phase and you'll be treated to a cutscene where a massive tentacle tears through the tower allowing you to continue onto the second phase by jumping down the tentacle hole. You'll arrive in a Moon Flayer colony, and this is where you'll find Zevlor.
Look around the Mind Flayer Colony and you'll discover a room in which Mind Flayers are being created, but you'll also discover that there are still people in those tubes. By pressing the Neural Apparatus you'll be given the choice to either purge the pods (effectively killing everything in the room) or open the pods, which will free the Mind Flayers but also free everybody inside the pods.
You'll have to fight the few Mind Flayers that have been freed but the fight should be rather trivial at your current level, especially seeing as you've also freed Zevlor and his friends who will join you in your fight. Defeat the Mind Flayers and then Zevlor will talk to you and thank you for saving him.