Armor: Heavy
Hit Points: 150
Ground Attack: 20
Air Attack: 0
Attack Range: 8
Gas Required: 100
Minerals Required: 50

Guardians are actually Mutalisks that have metamorphosed after entering a cocooned state. You must earn the ability to create Guardians, and this usually won't happen until your base is fairly well-established. The Guardian is a bomber. Its sole purpose is to hurl explosive gobs of acid at ground targets. Its awesome attack power (20) packs enough of a wallop to take out a Missile Turret in 10 hits (or 1 hit each from a group of 10 Guadrians, personal experience, as the victom).

Guardians work best when used in groups of 10 or more. A single volley from such a group can destroy any enemy unit that has 200 or fewer hit points. Of course, 12 Guardians bombing an enemy base won't bomb if for long if the enemy attacks with air units; The Guardian is air-to-ground only. This is why it's important to have Mutalisks standing by to defend the Guardians.

Expense is another limiting factor. Creating a Guardian not only costs 100 gas and 50 minerals, but you must metamorphose it from a Mutalisk, which has a price tag of 100 gas and 150 minerals. This means creating a Guardian costs 200 gas and 150 minerals altogether (ouch), so pretecting that investment is very important.

Mutalisks can also metamorph into another form, which is believed to be based on nesting form of the Mantis Screamer. The Zerg Guardian has a thicker armored carapace and attacks by lobbing explosive gobs of acid which spray. This acid can only be directed at targets on the ground below. Guardians have no natural defenses against aerial opponents.