Cloak is a defensive spell used by the Terran Ghost and Banshee which renders a unit invisible. The Spectre in the Campaign is also able to cloak, though it is not available in Multiplayer. Similar to a burrowed Zerg unit, a cloaked unit can be distinguished by keen players without detection by a distorted, graphical reflection.
A cloaked unit can only be targeted by an enemy player with a detector. However, a cloaked unit can still be hit by EMP Round, Psionic Storm, Fungal Growth or a manually detonated Baneling. A cloaked unit that has been hit by Fungal Growth will be revealed for the 4 seconds of the Fungal Growth and can be targeted by all nearby units.
While cloaked the unit can still move, attack, patrol, and in the Ghost's case, cast EMP Round, Snipe and call down Tactical Nukes. However, during Cloak energy is consumed at a rate of 0.9 energy per tick and Cloak is disabled when the unit's energy depletes.
Cloak is used on Ghosts and Banshees to hide them from normal vision where only detecting units can see them. Either unit, when combined with Cloak, is capable of performing extraordinary harassment. With Ghosts, Cloak is typically used while calling down nuclear strikes. Banshees can use Cloak while harassing with great results. Often Cloak will grant the players Banshee harassment a new life, as the research timing completes in the middle of the harass.
This gives the Banshee user extra incentive to prevent Sensors like Photon Cannons and Missile Turrets from building, and the Banshee user may target these during their initial harassment. Using cloaked Banshees against un-prepared opponents can end games very quickly by dealing massive economic damage.
Cloak can be used on Ghosts at key moments where the Ghosts are vulnerable to High Templar's Feedback, preventing them from being targeted. This will succeed if the opponent does not have an Observer to detect the Ghosts within range. This gives the player the advantage of being able to use EMP on the opponents forces freely.
Cloak magnifies the usefulness of the ghost and banshee in TvT, especially when used against a Terran mech army. A Ghost's Cloak in combination with a Tactical Nuke exploits the lack of mobility of a tank-heavy army. Cloak forces the Terran opponent to either use a Scanner Sweep or reposition, opening a timing window for a counter-attack by the harassing player. Cloaked Banshees have a similar effect for their strength against an immobile mech army. Cloaked Banshees force the opposing Terran to use Scanner Sweeps or Missile Turrets in combination with anti-air in order to prevent harassment.
Since Zerg is known for being a gas heavy race, they often have bare minimal detection from their Overseers. Because of this, Cloak can be quite effective to harass or in combination with abilities like Snipe or Tactical Nuke.
In Wings of Liberty and Heart of the Swarm
In Wings of Liberty, the Banshee Cloaking Field upgrade cost 200 minerals and 200 gas.
Due to the change of timing in Legacy of the Void, the timings are different in the last expansion than in Wings of Liberty and Heart of the Swarm. In the previous expansions, the personal cloak drained 0.9 energy per second after the initial 25 energy cost. The research took 120 seconds for the Ghost, and 110 seconds for the Banshee.