If you’re exploring the mysterious Oldest House thoroughly in Control, you’ll quickly encounter a strange substance called Mold. This alien fungus damages Jesse the moment she attempts to enter — and the Mold seemingly blocks access to rooms with lots of bonus treasure. If you’re aiming to fully explore the vast expanses of the Oldest House, you’ll need to earn yourself a Mold Immunity pill.
To do that, you have to unlock the side-quest ‘Old Growth’ — which I don’t recommend doing until very late in the game. The enemies in ‘Old Growth’ are the highest level you’ll see in the standard game, and when you finally get to venture deeper into the Pit, you’ll find the game’s most powerful opponents.
If you’re curious how to enter the Mold, here’s how to become immune.
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How To Unlock Mold Immunity | ‘Old Growth’ Quest Guide
The ‘Old Growth‘ quest begins late in the story. Emily Pope will ask you to visit Dr. Underhill beneath Central Research. I recommend waiting until after you’ve unlocked the Levitate Power, or even after completing the main story before returning to this area.
- NOTE: There is a Control Point in the unmapped Mold Threshold. From the entrance into the massive chamber, float up and left to find it. If you die, it’ll make return trips much faster.
The entrance to Dr. Underhill’s lab is found on the bottom floor of Central Research. Find the strange mold growth in the corner, and you’ll find a deep hole. Glide down to the bottom of the hole, then talk to Dr. Underhill — she’ll request five mold samples. To unlock Mold Immunity, you must bring her these samples.
- Mold Sample Locations:
- Type A: Spot the stairs in the upper back-left corner of the giant chamber. Take the stairs up to find the Control Point, then follow the dead bodies to an alcove with this sample.
- Type B: From the entrance, go to the back-right and drop down to find a sign that says ‘restrooms’ — enter this path to find a pile of toilets. Climb up to an alcove with the mold.
- Type C: In the lower far back-right corner of the large chamber, there’s a dark entrance that leads to a doorway marked “Lab 5” — the mold sample is inside.
- Type D: Straight ahead from the large pit entrance, there’s a staircase on the raised upper-left platform. The mold sample is under the stairs.
- Type E: Found near the entrance. In the large chamber, look down at the pit with spotlights. There’s a single raise platform with a desk on it — the mold sample is there.
Bring the samples back to Dr. Underhill, and she’ll give you an immunity pill. Now you’ll be able to survive in Mold areas! You can go back and explore areas you’ve missed, or drop deeper into the Mold zone.
Deeper into the pit, you’ll encounter extremely high level Mold Hosts and fight the source of the Mold, a creature called Mold-1. It’s very tough, so come prepared for a fight. Check out our bosses guide for more details on how to defeat Mold-1.