The developers of Baldur’s Gate 3 designed most questlines so that they may be completed in multiple ways. Thus, giving the players more freedom in how they approach situations. This guide represents one method that is confirmed to unlock this achievement.
A full achievement guide is available here:
https://tigorestips.com/dnd/baldurs-gate-3-achievements-trop...Create a manual save before going down this path.
Open Hand Temple
Optional Step: When you reach the beginning of Act 3, head over to the Open Hand Temple on the west side of the area. There you will discover a murder while talking with Sister Yannis. Agree to help investigate and gain entry to the 3rd floor of Fraygo’s Flophouse where you will find a Bloodstained Parchment on a desk hidden behind a wardrobe. Next, meet with Valeria in Sharess’ Caress and obtain a pass for the Lower City. Let the guards blocking the Lower City know that you are investigating a series of murders and they will let you through.
Lower City
Once you’re in the Lower City, you will have markers on your map showing where the remaining targets are located. Kill a target and you will be approached about the Assassins of Bhaal. Kill another and you will be given the passphrase to enter their lair. Make sure you grab the hand of one of the victims as proof. The door to the crypt is revealed after pressing a button hidden behind a painting next to the quest marker.
Inside the crypt, you will need to take out your competitor. Then, agree to the ritual and follow the promptings. You may want to ungroup from your party and leave them behind so they don’t disapprove of your choices. If the bathing cutscene doesn’t trigger after killing the final target, interact with Sarevok to start it. The Murder in Baldur’s Gate achievement or trophy will unlock after rising from the pool.
After becoming an Unholy Assassin of Bhaal, you will now have access to reach the Temple of Bhaal.
Finding the Temple of Bhaal
The Temple of Bhaal is located in the sewers under the Lower City. After becoming an Unholy Assassin of Bhaal, you can gain entry through the door next to the Undercity Ruins waypoint. While interacting with the door, let it know that you are an Unholy Assassin of Bhaal (“I have proven my faith…”) and show it the Amulet of Bhaal.
Once you enter the door, you will notice the game auto saving. This is because you are about to be ambushed. This can be avoided by using a potion of invisibility on a fighter or similar character who can deal massive damage and take it as well. Have the character run to the top tower across the bridge and solo kill the Farslayer of Bhaal Ghislev which will end the fight. This enemy will teleport off the tower and other enemies will join the fight. Be ready to focus all effort on the Farslayer.
Temple of Bhaal
After the Farslayer is defeated, all other enemies will vanish. You should be in the northeast corner of the room, next to a large archway which is the pay to continue forward. Make sure you long rest before continuing. Then, enter the next area and work your way down the stairs on the right/east. They will lead to the door of Bhaal’s Temple after you pass by the waypoint. Use the Amulet of Bhaal once again to open this door, gaining entry to the temple.
Now, head down to the large circular area with a table on the east side of the room. Say whatever you want during the interaction with Orin. At some point, she will ask her father to join her and the battle will begin. Ignore all other targets and only attack Orin until she drops. Doing so will unlock the First Blood achievement.