The Undercity Ruins are a part of the widespread tunnel system in the sewers beneath the city of Baldur’s Gate. After going inside the Guildhall and slogging your way through the sewers, you reach the Undercity Ruins waypoint in Baldur’s Gate 3. At the waypoint, taking a right will take you into a large and open space surrounded by cliffs and a massive building. If you passed a perception check, though, your party will recognize this area is a giant trap, and there are Bhaal Reapers waiting for you.
This is no ordinary fight in BG3. There are over a dozen enemies waiting for you atop the cliffs and in the windows of the building to the north. However, one main enemy, the Farlsayer of Bhaal Ghislev, is the key to the entire fight.
You must progress past this area to explore more of the Undercity and access the Temple of Bhaal. Here’s how.
Fighting the Bhaal Reapers in the Undercity Ruins of Baldur’s Gate 3
My first advice is to have a single character separate from your party and use an invisibility spell, scroll, or potion. You might want to bring more than one potion or scroll so you can replenish the invisibility if you run out. Once your character is invisible, progress down the slope that leads into the area where you are ambushed by the Bhaal Reapers.
With this character still invisible, go across the broken column that acts as a bridge and then go up the ladder found on your right after making it across. Then, go up the next ladder and right behind the stone block with the blue circle on it, as seen in the screenshot below. Make your character wait there while the rest of your party joins the fight.
As soon as the rest of your party enters the area, combat will ensure. Your character on the platform will not be invisible anymore and will have a direct line of sight to the Farlsayer of Bhaal Ghislev on the blue stone circle. While the entire area is teeming with enemies, killing the Farlsayer will make all of them disappear. so, your top priority is to kill this enemy.
Unfortunately, he doesn’t have any weaknesses. My strategy was to simply keep peppering him with any spell or attack I had available. They will all only deal a few damage each regardless, unless you can manage a critical hit. After taking some damage, though, the Farlsayer will transport himself to the doorway below the ladders and also spawn a new enemy in front of him.
Keep your character on the platform up there and attack from above. As for your other characters, I do not recommend trying to send them across the bridge to get to the Farslayer. There are enemies in the building windows who will shoot Roaring Thunder arrows at you, which cause you to be knocked back and fall off the bridge. There are also multiple enemies on the ground who will do everything they can to get you to stay off the bridge.
As such, your main strategy needs to be having your lone character on the platform damage the Farslayer until he dies. It took me hours to win this fight against the Bhaal Reapers, but this strategy did eventually work. Once the Farslayer dies, the rest of the enemies will say the “trial has been passed,” and will begin disappearing.
You can now move to the spot where the Farslayer was and keep exploring the rest of the Undercity Ruins and the Temple of Bhaal in Baldur’s Gate 3.