Phasing Zombies are a enemy introduced in Moon. They appear to be Crawler Zombies that have been granted the ability to teleport. They will phase in and out of the player's sight, and some do not explode upon death. They perform a notably unique animation when hit by the Wave Gun, as opposed to normal Zombies. In appearance, they look the same as Crawler Zombies. Phasing Zombies do not explode in low gravity and have slightly less health than Crawler Zombies.

If you are wearing a P.E.S, you can't get hurt by the actual gas, although you can get hurt [and blinded] by the initial explosion.