Old Growth – Mold Removal Ritual Division
Once you have finished the Old Growth side mission Ahti will ask you to eradicate Mold Hosts around the facility. To start, Levitate up to the area above the entrance to the elevator shaft in Central Research.
Kill the Mold Host and fast travel to Active Threshold to complete this side quest. You’ll earn some Ability Points and a material.
The First Host
Ahti wants you to eliminate three enemies that have been infected with mold and can be found in different locations. The first one is chilling in the Astral Exhibition, the second is in the Extrasensory Lab, and the third is in the passageway leading to Parakinesiology.
First, head to Central Research and fast travel to the Control Point. You should see a large amount of blue-colored Mold on the ground floor near a hole in the wall. To get in, you’ll need to have Levitate unlocked. Jump into the hole and make your way through the area, taking care of Mold Host spores along the way.
After clearing the area, you’ll find a sealed door near the entrance to the Ritual Division lab. Interact with the monitors inside to see what position the doors need to be in to open, and then interact with them to gain access to the underground room Mirror Testing (Clearance Level 6). Destroy all six green Mold ball creatures while there, and Ahti will reward you.
The Second Host
After killing the Rubber Duck and informing Underhill of its destruction, she’ll ask you to track down several Mold Hosts that are still loose around the facility. You’ll have to kill three infected targets. They’re spread across different areas, but can be located thanks to the presence of mold that appears on walls and floors.
The first is in the Extrasensory Lab, in the room with wooden racks. The second is in the Ritual Division office, and the third can be found in the bathroom outside the Luck & Probability room.
After destroying the two Mold Hosts in the area, a large green and glowing ball will spawn, which you can destroy using your Service Weapon or by launching objects at it. Defeating this boss rewards you with four ability points and an additional material. After claiming this reward, fast travel back to Central Research and use Levitation to mitigate the fall damage. This will bring you to the control point in Ritual Division.
The Third Host
To find the third infected enemy, head to Central Research and enter the elevator shaft down to Dr. Underhill’s lab (use Levitation to mitigate the fall damage). When you reach the bottom, turn around and follow the corridor around. The Mold Host is in the room labelled ‘Lab 1.’ You can also reach this area by taking the lift down from the main staircase in the Astral Exhibition.
Once you’ve entered the room, clear out the mold enemies in the tunnels, grabbing a loot container along the way. Examine the tape recorder on the table to acquire Threshold Log 2.
The next area is the restrooms, accessible from the same way you reached the first one in Central Research. Clear out the enemies and then examine the restroom door to unlock the Hidden Location. Activating this will spawn Mold-1, which you can defeat by shooting it in the head with a Pierce weapon. This will complete the side mission and earn you 4 Ability Points.
The Final Host
After killing all the Mold Hosts in this area you can turn in this side mission to Dr Underhill. She will thank you profusely for your help, and give you some tasty rewards and skill points as compensation.
Once you’re back in the Research division, fast travel to the Control Point and head into Central Research. Look for a hole in the floor littered with blue-colored Mold, but remember that you can only jump in it after unlocking the Levitate Ability. Drop down and navigate around the pit, defeating any Mold Hosts you encounter.
Once you’re clear, Levitate across to a platform near a desk in the room, and collect Mold Sample E. Then look down to see another opening in the wall, and enter it. The next room is a disused restroom, and the final Mold Host can be found inside one of the toilets. It can be a little tricky to find, so just keep exploring until you discover it.