- "Just like Maxis predicted! They think I am one of them!"
- — Richtofen, upon picking a Zombie Blood power-up
- "Zombie Blood!"
- — Demonic Announcer
Zombie Blood is a power-up that appears in Origins. It causes the player to be masked in a red fog and disguised as a zombie, thus Zombie enemies ignore the player (similarly to the Vulture Aid gas ability). The Power-Up itself appears as a bag of blood, lasts for 30 seconds, and can only be used by the player who picks it up. It also slightly increases the player's field of view.
A free Zombie Blood is always given as a reward in the Rituals of the Ancients box near Generator 1 after it is first turned on, except on solo, where it is replaced with a Double Points (the exception does not include playing custom match solo).
Players can obtain a free Zombie Blood, once per round, unless it is raining, by shooting three flaming carts around the Excavation Site with the Staff of Ice (upgraded or not). The Zombie Blood will appear next to some scaffolding by the Pack-a-Punch Machine.
When in Zombie Blood mode, Samantha may talk to the player in a demonic voice, giving hints on how to obtain the staff parts, whispering the easter egg step as players progress it, and even talking personally to each character trying to convince him to free her by making threats, promises, and talking about their history and the dark future that is about to come.
The Zombie Blood power-up returns in Blood of the Dead, where it appears if the player enters the code '872' into the digital number display within the Citadel Tunnels.
- Master of Disguise (15 /Bronze Trophy ) - In Origins, use Zombie Blood to revive three players and activate a generator in one game.
- Saving the Day... All Day (20 /Bronze Trophy ) - In Origins, revive another player four different ways in one game.
- Little Lost Girl (75 /Silver Trophy ) - In Origins, release Samantha.
- In The Crazy Place there is a message on one of the middle pillars that can only be seen in Zombie Blood mode, saying "Follow the steps".
- Several players often feel as if the Zombie Blood power-up accelerates the player's movement speed. However, the speed remains the same, and it's only an illusion caused by the change in the Field of View.
- The icon for the Achievement Acid Drip in Mob of the Dead has a similar appearance to the Zombie Blood power-up.