Mysterious Keys X and O are multi‑use, consumable keys that open “marked” rooms on the overworld. They behave like limited‑durability items: each key has a set number of uses (around 10 for these marked keys), and once those uses are gone, the key is spent. Consumable keys with a durability bar cannot be registered for permanent access.
| Item | Type | Uses | Registerable | Primary door/room | Notable rewards behind it |
|---|---|---|---|---|---|
| Mysterious Key X | Consumable key | Multi‑use (~10) | No | X Marked Room (Farm Town construction site) | Blue and Black keycards, high‑tier loot (weapons, GPUs), more keys |
| Mysterious Key O | Consumable key | 10 uses | No | O Marked Room | Color keycards (including Red/Black/Green/Yellow), assorted high‑value loot |
Where to use Mystery Key X
Take Key X to Farm Town. In the construction site there’s a locked building marked with an X — that’s the door it opens. Inside is a “marked room” loot pool designed for progression: expect a compact space with dense containers and the chance at rare drops.
What to expect from marked rooms (X and O)
- Progression cards: The X room can drop Blue and Black keycards. The O room can also roll color cards, including Red, Black, Green, and Yellow.
- High‑tier gear: Weapons and rare components are in the mix. Examples seen from X runs include rifles like MDR/M14 and components like GPUs.
- More keys: It’s common to walk out with additional keys, including more marked keys.
If you’re pushing toward late‑game loot, these rooms are a shortcut: they compress a lot of the game’s rare rolls into a couple of chests and containers.
How marked rooms feed J‑Labs keycard progression
Marked rooms are a reliable way to bootstrap your J‑Labs access chain. Blue and Black keycards can drop from the X room, and the Blue room inside J‑Labs can in turn drop the Red keycard. With a few strong marked‑room runs, you can assemble the color cards needed to start clearing the high‑end Labs rooms and their end‑game loot pools.
Finding or buying X and O keys
- World loot: Keys can appear in ordinary loot containers. Jackets and wall‑mounted coats are especially worth checking. Envelopes can also contain marked keys.
- Early homes: It’s possible to find marked keys in houses near early quest hubs.
- Vendors: The Farm Town merchant on the hill near the teleport (north of the sanatorium) can occasionally sell the O Key, X Key, and even a Black keycard.
- Black Market: Prices fluctuate — you may see Key X listed in the low six figures or receive very high offers to buy yours.
Registerable keys vs. consumables
Later, you’ll unlock a facility that permanently registers eligible keys so you no longer have to carry them. Consumable keys — easy to spot by their durability bar — cannot be registered. Mystery Keys X and O fall into that consumable category, so expect to carry and spend them until they break.
Avoid losing your keys
There’s a risk of losing marked keys if they’re left in base storage and you sleep. To protect them, keep keys on your character or stash them in your dog’s bag before turning in for the night. This simple habit prevents accidental loss and saves rare runs from being blocked.
Should you sell or use Mystery Key X?
Sell if you urgently need cash and have other progression paths ready. Offers can be substantial, and you’ll still find X again through loot or vendors. Use if you want faster progression into J‑Labs and end‑game loot. A handful of X room runs can net multiple color cards, rare weapons, and high‑value components — value that often exceeds a one‑time sale.
Practical split: run a few X uses to secure core cards (Blue/Black, plus a shot at Red through Blue room), then offload extra X keys or partial durability copies when your kit is stable.
Difficulty and loot, briefly
Loot quality appears to scale with difficulty. If you’re hunting keycards and top‑tier drops, higher difficulty settings can make marked room runs and Labs rooms more rewarding.
The fast path is simple: secure Mystery Key X, open the Farm Town marked room, prioritize pulling Blue and Black keycards, and pivot into J‑Labs where the Blue room can yield Red. Along the way, treat X/O as spendable tools, not trophies — and keep them out of base storage before you sleep.
