Overshield

An overshield is a form of Covenant-developed technology that strengthens the user's energy shielding system

Overview
The overshield technology was developed to enhance the Covenant's Sangheili warriors' personal shielding system. Although designed in mind for the Covenant shielding system, the technology can also be used by anyone utilizing a personal shielding system such as a SPARTAN-II in a MJOLNIR armor.

Gameplay
In Halo: Combat Evolved and Halo 2, the overshield boosts the player's shields to 300%. This was reduced to 200% in Halo 3. In Halo: Reach 's Anniversary Map Pack, the shields are once again boosted to 300%; however players now spout a trail of flames, further revealing their position. The trail also forms if the player enters a vehicle.

In campaign mode, the overshield is reduced only when the player takes damage. In multiplayer, the overshield is not only subjected to the same rule in campaign mode but also gradually depletes overtime. Due to its reductive nature, the overshield is only useful for a short period in multiplayer; the overshield slowly loses its strength over prolonged duration. Like the standard energy shield, the overshield can be fully depleted by an overcharged Plasma Pistol.

It takes approximately three seconds to overcharge the energy shields once picked up. During this short period, the player is invulnerable to all forms of attacks, save for a melee attack from behind. The player's normal shield does not take damage until the overshield is completely depleted (although any damage overlapping from something destroying the overshield such as an explosion from a grenade will also do damage to the player's normal shield).

In Halo 2 and Halo 3, the wearer is awarded a visual effect which gives off a full-body glowing effect. This visual effect negates the effects of an active camouflage and makes the wearer more visible to other players, often drawing unwanted attention.

Appearances
In Halo: Combat Evolved, the overshield appears as a glowing red orb of energy encased in a clear glass cube. The same design is used in Halo 2; this time, however, the orb and cube are gold in color. The design of the overshield in Halo 3 differs and shares some resemblances from previous titles: the orb appears as a glowing red orb of energy, without a glass cube encasing it.

After picking up an overshield in Halo: Combat Evolved, the player's HUD shield display changes color from blue to red to yellow. The same is present in Halo 2, though the shield display changes color from blue to red to green instead of to yellow. In Halo 3 however, the shield display only changes from blue to red. This gives the indication that each color represents one layer of shield.

The overshield can only be found in campaign mode in Halo: Combat Evolved. It is absent from Halo 2 's and Halo 3 's campaign mode (replaced by Invincibility. The overshield makes an appearance in Halo 3: ODST as a shielding effect awarded to those within the vicinity of an Engineer; Covenant and UNSC units are provided an additional layer of protection because of the overshield ability.

Trivia

 * The Black Eye Skull in Halo 2 allows the player to achieve overshields through meleeing enemies which restores the player's shield.
 * In Halo 3, you can pick up the overshield (or active camouflage) as equipment if you have a piece of equipment and hold your equipment change button (default RB) and barely touch the overshield. Then if you die you drop the overshield, or if you pick up another piece of equipment you will drop/pickup the overshield, allowing you to surprise your enemies. This only works on matchmaking.
 * The overshield was most likely inspired by a similar device found in the Marathon series. Using this device in the Marathon Series causes up to two additional layers of heath to be added (yellow/purple).

List of appearances

 * Halo: Combat Evolved
 * Halo: Combat Evolved Anniversary
 * Halo 2
 * Halo 3
 * Halo 3: ODST
 * Halo: Reach
 * Halo 4