The Serum Puzzle is a multi-stage challenge that blocks progress in the Easter Egg on BO7 Zombies. The task asks you to collect four rare artifacts, work out their correct order at Yuri’s Lab, and then survive a final lockdown while the serum mixes. Many teams run practice sessions in a CoD BO7 Bot Lobby to memorize routes and rehearse the hardest parts before tackling the full sequence in live matches.
Phase One — Gathering the Four Artifacts
The first step is to find the Powder of the Forgotten, the Jar of Spores, the Widow’s Lantern, and the Mysterious Limb. Each item hides in a specific place and needs a different approach. Go to Taylor Shop and shoot the intact mirror until it breaks to get the Powder. Then travel to Blackwater Cabin and pick up the Jar of Spores from inside the building. At Vandorn Farm, grow the local spores by interacting with the nearby planters until the Widow’s Lantern appears. For the Mysterious Limb, track down a Zersa bear and use Ol’ Tessie’s beam weapon to finish it off; the limb drops after the bear falls.
Phase Two — Reading the Chalkboard in Yuri’s Lab
After you gather the four pieces, bring them to Yuri’s Lab to decode the recipe. The lab’s chalkboard shows symbols or a small sequence that tells you how to place the artifacts in the serum machine. Match the symbol on each item to the board. Place the artifacts in the exact order the board shows. Take a moment to double-check the board and confirm the match before you interact with the machine.
Phase Three — Input and Blood Sacrifice
Approach the serum machine and insert the four artifacts in the sequence you read. After the items are in place, the machine asks for a blood sacrifice to start the final blend. Use a blood item or perform the required action to feed the machine. Once you begin the blood input, the serum enters a timed cycle and the lock will fall over the room. You cannot leave the machine area without breaking the process, so set up defenses and prepare to hold the line while the serum finishes mixing. The machine shows a progress meter; watch that meter closely and do not interrupt the sequence.
The Lockdown — Defense and Survival Tips
When the lockdown starts, expect heavy and frequent spawns that push straight for the machine. Use choke points near Yuri’s Lab and keep a few grenades or area abilities ready for large clusters. Save mobility tools to move between cover if the room becomes overwhelmed. If you have deployables, place them on the main approach and near the terminal so they buy extra seconds. Keep ammo and healing items on hand; the lockdown can drain your resources fast.
Practice Runs and Using the Bot Lobby
If your team wants to reduce mistakes, rehearse each step in a CoD BO7 Bot Lobbies buy. Use the Bot Lobby to practice breaking the mirror, growing spores, operating Ol’ Tessie on a Zersa bear, and matching the chalkboard symbols under low pressure. Drill the lockdown defense until your team knows the best positions and who covers which angles.
After the Serum — What Opens Next
When you survive the lockdown and the serum completes, Yuri’s Lab will dispense the anti-serum and unlock the next stage of the Easter Egg. The completed serum often enables new interactions, opens access to unique items, or triggers the following ritual step in the quest line. Once you have the serum, move quickly but carefully to the next objective.
