Shadow

The Shadow is a zombie in and. Walls and barricades will not affect them, as they can move through anything. They can count as a boss, as they have a health bar. In SAS: Zombie Assault 4, there's a zombie modifier named "Dark Minion" which basically turns zombies into shadows.

Tactics

 * The AUG PARA works good on it (SAS 3).
 * The JKH 0.887 CAW is a perfect counter against Shadows due to its high damage and the ability to shoot through walls.
 * Keep running and keep shooting at it, and eventually it will die. Their high movement speed means using weak weapons like pistols or low tier submachine guns will get players killed.
 * Throwing a Cryo Grenade at it and using a high powered weapon also works well.
 * Any shotgun works well on the shadows.

SAS Zombie Assault Tower Defense
In SAS Zombie Assault Tower Defense, the Shadow makes its first appearance on round 15. It has the ability to walk through your defenses, but it can not walk through buildings. This also means it won't harm barricades or defenses. It appears to have more health than in SAS 3.

Trivia

 * The idea of the shadow may have come from the demons called Shadow people who feed off of a person's negativity during sleep paralysis.
 * The Shadow's red eyes darken when killed.
 * This zombie is the second fastest zombie in the game, with Sprinter taking first place.
 * The Dark Minion buff in SAS 4 is based off the shadow of SAS 3.