The Mystery is a very dangerous zombie that first appears on wave 16 of Easy and Normal modes. It is a zombie that moves as fast as a normal and randomly spawns a zombie upon death. It can either spawn a Normal, Speedy, Slow, Hidden, or a Normal Boss upon death. Its tougher counterpart on Hard and Insane modes is the Ultra Mystery.
It is identifiable by the orange question mark in the center of its torso and its translucent green body.
The Mystery is best dealt with by killing it early on; this is most easily achieved with high amounts of splash damage or rapid-fire, which can also kill the weaker zombies it deploys. Despite their ability to sometimes spawn a Normal Boss, they should be easily dealt with due to a few spawning in previous waves.
- (??/??/19) Added to the game as Mystery 1. The initial appearance was on wave 13 (all difficulties).
- (7/15/19) Mystery 1 now has a green body.
- (8/2/19) Mystery 1 got a nerf. Normal Bosses are now more rare from Mystery 1.
- (10/13/19) Zombie rebalanced as part of the difficulty and wave rework.
- Name changed from Mystery 1 to Mystery.
- Now appears on wave 16 of Easy and Normal modes only.
- HP no longer scales with the number of players.