Invincibility

Invincibility is an equipment item featured in Halo 3 and Halo 3: ODST. It gives the user a brief period of invulnerability, lasting for about 10 seconds. In order to obtain it, the player is required to kill a Jiralhanae Chieftain without having it activated, although in some rare cases, it can be found lying around in certain levels.

Operation
When activated, the player is covered in shining white bands. It is possessed by all Brute Chieftains that wield Gravity Hammers unhindered, but not the Brute War Chieftains. Shooting them when it is activated is simply useless, as you cannot harm them except by performing an assassination, which, done correctly, will kill them Invincibility or not. In Campaign, it can be found on some dead Brute Chieftains that have not used the power-up, but this is a rare occurrence, as they will usually activate it the instant they are attacked. In addition to being obtainable from dead Brute Chieftains, there is an Invincibility in the level "Halo" on Easy, Normal, and Heroic difficulties. After going up the staircase, face the middle of the door, then turn around the other way and walk into the tunnel. This makes the battle with 343 Guilty Spark much easier, since you cannot get hit by the powerful beam.

It has a similar appearance to the Cloaking equipment, except that it glows a gold color, rather than a cool blue color. Its symbol on the HUD is two overlapping, intersecting ovals with a dot at the center.

It is not present in multiplayer, unless you edit game-play options where you can make players invincible. However, do note that the Guardians can still kill you; apart from them your only real danger is from being assassinated.

Disadvantages

 * Players or NPCs who have activated the Invincibility equipment can still be killed by assassination, get smashed by falling objects, getting splattered, or fall to their death from a great height.
 * It only lasts for about 10 seconds, so it should only be used as a last resort, or when entering a particularly difficult part of a level.
 * It is still visible even with the aid of cloaking or Active Camouflage.

Trivia
In Halo 3: ODST, Invincibility makes Chieftains glow an aquamarine color, instead of the original white. This may have something to do with the lighting effects and color pallet of the game, which tend to be more rich in color and high in contrast, as opposed to Halo 3's pallet, which is more white or faded. It could also be effected by the HUD used by ODST's, which has several differences from the HUD of a SPARTAN-II, most notably the inclusion of systems for acquiring and tracking targets (which tend to change the appearance of the target as seen by the player).
 * The Invincibility symbol resembles a Helium atom. This may be because the power that is exerted by this equipment can be compared to that of an atom, (or sub-atomic and elementary particle) when disintegrated, 'split', or charged.
 * If you make the Arbiter an enemy by knocking him out/killing allies, and use the Invincibility, he can still kill you with one shot with whatever weapon he is holding. Strangely, blue sparks will fly out of your corpse like when you disable a vehicle with a Power Drain or overcharged Plasma Pistol shot.
 * Also in Halo 3: ODST, Chieftains tend to activate their Invincibility the moment any heavy weapon hits them, thus negating or toning down its effect.
 * The Invincibility is not available in Halo 3: ODST or out side of Halo 3 's Campaign. That said, game code for the Invincibility is present in the multiplayer map Cold Storage, which means that modders can utilize them.
 * Brute Chieftains who have activated their Invincibility can still be assassinated and splattered.
 * Invincibility is a reworked version of the Overshield seen in Halo Combat Evolved and Halo 2, but does not run out like the Overshield.