Invincibility

Invincibility is an equipment featured in Halo 3, 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 Brute Chieftain without having it activated, and in some rare cases, it can be found just lying around in certain levels. Like the Gravity Hammer is to the Fist of Rukt, this equipment originates from Tartarus's Modified Invincibility.

Operation
When activated, the player is covered in shining white bands. It is known to be possessed by all Brute Chieftains that wield a Gravity Hammer unhindered, but not the Brute War Chieftains. Shooting them when it is activated is simply useless, as you cannot harm them in any way. In Campaign, it can be found on some dead Brute Chieftains that haven't 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 from behind.

Disadvantages

 * Players, or AIs who have activated the Invincible equipment can still be killed by being assassinated, crushed by large objects, or falling from a great height. Also, the Invincibility can be drained by Infection Forms.
 * 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, but not the first chance you get.
 * When the equipment is deployed, it makes the player glow a gold/white/purple color, much like an Overshield, therefore making you more visible when used and might attract unwanted attention towards you.
 * It is still visible even with the aid of cloaking or Active Camouflage.

Trivia

 * The easiest way to get one, is to kill a Brute Chieftain in one shot or from far away using a Sniper Rifle, which obviously doesn't give him the chance to use it. Notable ways include the Spartan Laser and Rocket Launcher, and on easier difficulties, a Beam Rifle or Sniper Rifle head shot. Grenades hardly ever make a one hit on them, with the exception of the Incendiary grenade.
 * The Invincibility has an analogous effect to Tartarus's shields, which he uses in the last level of Halo 2.
 * 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 killing him/allies, and use the Invincibility, he can still kill you with one plasma bolt.
 * In Halo 3: ODST, Invincibility makes Chieftains glow an aquamarine color, instead of the original white.
 * 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.
 * You cannot acquire this power up online.