Changeling

From The StarCraft 2 Wiki

Changelings are a non-descript Zerg unit that will assume the exact physical appearance of a unit of another player, to infiltrate their base. Primarily made as a scouting unit.

[edit] Gameplay

StarCraft II Unit [e]
Changeling
Race:	Zerg, Tier 2
Role:	Infiltration Scouting
Unit Statistics
Size:	Small
Type:	Biological
Speed:	Varying
Transport Slots:	Varying
Hit Points:	x
Plasma Shields:	N/A
Energy Points:	N/A
Offence
Armament:	N/A
Ground Attack:	N/A
Air Attack:	N/A
Range:	N/A
Defence
Armor:	x
Sight:	x
Cooldown:	N/A
Special Abilities
Production
Hotkey:	x
Supply:	1
Resources:	x x
Build Time:	x
Produced by:	Overseer
Prerequisite:	Overseer

Overseers can create a Changeling by spending energy. The Changeling is a small unstable Zerg creature with timed life. When he gets near an enemy structure or unit he will change shape into the correct basic unit type and color to match that player. So if you get near a Blue Barracks you become a Blue Marine. If you get near a Red Stalker you become a Red Zealot, etc.

Enemy players cannot control the Changeling, it's still owned and controlled by the Zerg player who created it. It is very vulnerable and can be killed by a single hit from just about anything. The Changeling cannot fight. He is just a shapeshifter, when he looks like a Marine that gun in his hand isn't "real".

You can see that something is a Changeling by mousing over the unit, by trying (and failing) to drag select or by selecting the unit and seeing the name and portrait.

[edit] Development

The Changeling was briefly cancelled due to being too powerful, but was restored into the game as a very weak, quickly expiring unit, unable to use any unit abilities.