Ashes of the Damned is one of the biggest quests in Call of Duty: Black Ops 7 Zombies, and the Serum Puzzle is a major objective within its Main Quest.
The puzzle can look confusing because the ingredients are spread across the map and the final code changes between matches. Once you know what to collect and how Yuri’s Lab works, the process becomes much easier.
This guide focuses only on the serum step, without taking you through the entire Ashes of the Damned Easter Egg.
BO7 Zombies Serum Puzzle at a Glance
| Step | What You Need to Do |
| 1 | Obtain the Necrofluid Gauntlet and prepare the map |
| 2 | Collect all six serum ingredients |
| 3 | Take the ingredients to Yuri’s Lab |
| 4 | Reveal and decode the chalkboard symbols |
| 5 | Select three ingredients in the correct order |
| 6 | Add blood and survive the lab lockdown |
Step 1 – Start the Objective
Before making the serum, you need to progress far enough through the Ashes of the Damned Main Quest to obtain the Necrofluid Gauntlet.
You will also need access to the major locations around the map, including:
- Ashwood
- Blackwater Lake
- Vandorn Farm
- Zarya Cosmodrome
- The roads connecting each area
The serum step is not triggered by collecting three laboratory samples. Instead, you must gather six separate ingredients using different enemies, traps, quest items, and Ol’ Tessie upgrades.
Players exploring the wider game can find current modes, Zombies progression, camos, and related options through the Black Ops 7 main page.
The existing Yeti Dominos Bundle remains a separate cosmetic reward and is not required to complete the Serum Puzzle.
Step 2 – Find the Six Serum Ingredients
You need the following six items:
| Serum Ingredient | How to Get It |
| Powder of the Forgotten | Use Wisp Tea and the Necrofluid Gauntlet on the mirror in the Ashwood Tailor Shop |
| Widow’s Lantern | Place the Jar of Spores on the horse carcass near Vandorn Farm and return after three rounds |
| Human Bones | Cut the dripping foot from a hanging body in the Vandorn Farm barn, then burn it |
| Ravager Eyes | Kill a Ravager with the Saw Trap at Vandorn Farm |
| Hoard Husk Chunks | Destroy a purple roadside pod using Ol’ Tessie’s Abomination Beam |
| Mysterious Limb | Kill a Zursa with the Abomination Beam from Round 16 onward |
Powder of the Forgotten
Buy or obtain Wisp Tea, then head to the Tailor Shop in Ashwood.
Kill zombies in the mirror room until the Wisp activates the mirror. Shoot the revealed object with the Necrofluid Gauntlet to collect the Powder of the Forgotten.
Widow’s Lantern
Go to the Blackwater Lake cabin and collect the Jar of Spores near the kitchen sink.
Take it to the horse carcass on the road near Vandorn Farm. Interact with the horse, wait three rounds, and return to collect the Widow’s Lantern.
Start this step early because the three-round wait is unavoidable.
Human Bones
Enter the Vandorn Farm barn and look at the bodies hanging from the ceiling.
One body has blood dripping from its leg. Throw a Combat Axe at the foot, then use a Molotov to burn it. Collect the Human Bones that remain.
Ravager Eyes
Wait for a Ravager to appear at Vandorn Farm.
Activate the Saw Trap and lead the Ravager into it. When the trap kills the enemy, collect the Ravager Eyes.
Hoard Husk Chunks
Drive Ol’ Tessie along the roads between the main locations.
Look for a large glowing purple pod beside the road. Destroy it with the Abomination Beam and collect the Hoard Husk Chunks.
Mysterious Limb
The Mysterious Limb cannot normally be obtained until a Zursa begins spawning from Round 16 onward.
Use Ol’ Tessie’s Abomination Beam to land the final hit on the Zursa. If the beam gets the killing blow, the enemy drops the Mysterious Limb.
Players who still need stronger weapons or unlocked attachments can review the existing weapon max-level option separately.
Step 3 – Take the Ingredients to Yuri’s Lab
Once all six items are collected, travel to Zarya Cosmodrome.
Enter Yuri’s Lab in the southwestern section of the area. The ingredients will appear on the table inside the lab.
Interact with the Powder of the Forgotten. White smoke will reveal a randomized Pigpen-style cipher on the chalkboard behind the ingredients.
There is no universal three-button solution. The symbols and required ingredient order can change between games.
Step 4 – Decode the Chalkboard Symbols
The chalkboard shows three ingredient names through symbols.
Read the three entries from top to bottom and match each one with the corresponding item on the table.
The possible selectable ingredients include:
- Ravager Eyes
- Human Bones
- Hoard Husk Chunks
- Widow’s Lantern
- Mysterious Limb
Powder of the Forgotten is used to reveal the cipher, so it is not one of the three ingredients you select afterward.
Interact with the required items in the exact top-to-bottom order shown by the chalkboard.
Do not select ingredients randomly. A wrong choice fails the attempt and may force you to wait until the next round before trying again.
Step 5 – Add Blood to the Serum
When the three correct ingredients have been selected, the serum changes and a prompt appears on the central flask.
Interact with it to add blood.
Be careful: the player who adds the blood has their maximum health reduced to 75 HP for the rest of the match. The effect cannot be reversed during that session.
In co-op, choose the player who is most comfortable surviving with reduced health. In solo, make sure you have upgraded armor, a strong weapon, and useful equipment before interacting.
The MXR-17 loadout is primarily a Multiplayer setup, but its recoil and handling principles may still help when preparing a reliable weapon build.
Step 6 – Survive the Yuri’s Lab Lockdown
Adding blood locks the doors and starts a zombie defense event.
Stay inside Yuri’s Lab until the lockdown ends. The attack lasts roughly two minutes and can include heavy enemy pressure in a confined room.
Before starting:
- Pack-a-Punch your main weapon
- Upgrade its rarity
- Refill armor
- Carry a strong Tactical and Lethal
- Avoid beginning at the end of a difficult round
- Keep one escape path around the room clear
- Save Field Upgrades for the heaviest wave
Solo players should keep moving around the available space rather than standing beside the serum table. In co-op, split the room into firing directions so the team does not focus on one doorway.
The existing M15 Mod-0 build can provide another weapon reference, although you should still adjust the setup for Zombies damage and survival.
Once the lockdown ends, the serum step is complete and the Main Quest continues into its later objectives.
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Common Serum Puzzle Mistakes
Looking for Only Three Samples
There are six serum ingredients to collect. The three-item step happens only inside Yuri’s Lab, where the chalkboard cipher determines which three collected ingredients must be selected from top to bottom.
Searching Three Separate Laboratories
The ingredients are found around Ashwood, Blackwater Lake, Vandorn Farm, the roads, and enemy encounters. They are not stored in three generic laboratories.
Pressing Consoles in a Light Pattern
The final solution uses the chalkboard cipher and ingredient table. There is no universal three-console light sequence for this serum step.
Killing the Zursa Normally
The Abomination Beam must get the killing blow for the Mysterious Limb to drop.
Starting the Blood Step Unprepared
The player adding blood drops to 75 maximum HP, and the lab immediately becomes a dangerous enclosed defense area.
Final Thoughts
The Serum Puzzle becomes manageable once you separate its two parts: collecting all six ingredients and solving the randomized three-item sequence in Yuri’s Lab.
Gather the ingredients, reveal the chalkboard with the Powder of the Forgotten, choose the correct three items from top to bottom, and prepare carefully before adding blood. Survive the lockdown, and the Ashes of the Damned Main Quest can continue.
BO7 Zombies Serum Puzzle FAQs
How many serum ingredients are there?
There are six: Powder of the Forgotten, Widow’s Lantern, Human Bones, Ravager Eyes, Hoard Husk Chunks, and Mysterious Limb.
Where is Yuri’s Lab?
Yuri’s Lab is located in the southwestern part of Zarya Cosmodrome.
Is the serum code the same in every match?
No. The chalkboard solution is randomized, so read the symbols and select the three matching ingredients from top to bottom.
What happens if you choose the wrong ingredient?
The attempt fails, and you may need to advance to the next round before trying the sequence again.
Who should add blood in co-op?
Choose a well-prepared player because their maximum health is reduced to 75 HP for the rest of the session.
Can the Serum Puzzle be completed solo?
Yes. Upgrade your armor and weapon before adding blood, then keep moving during the Yuri’s Lab lockdown.
