Infected Brute Chieftain

The Flood Brute Chieftain is a glitch that can be found on the Halo 3 level,.

Walkthrough
It can be done by getting a Flood Infection Form onto a Brute Chieftain. These two do not normally exist in the same area. The only way to get them together is to kill all your allies outside the third tower in the level, while leaving some Flood Carrier Forms alive. Kill the Carriers and let the Infection Forms chase you up into the snow area. It is advised that you drive the Mongoose into the snow area; driving the Mongoose dramatically reduces the chances of being splattered by the Prowler. Kill the War Chieftain there and let the Flood take him over.

After being infected, the Chieftain's appearance does not change except for some Flood infection on his back. He retains all his normal combat abilities, including vehicle boarding. His shields stay down. The infected Chieftain attacks both the player and the Covenant nearby. The Chieftain is vulnerable to headshots and assassination.

Surprisingly, the Chieftain can pick up any weapon, even human weapons such as the Rocket Launcher. However, he cannot use all of the available weapons. For example, if he picks up the Energy Sword, he will charge at you, but he cannot use the sword to melee; he uses his fist instead.

This glitch can also effect Elites and Marines but you must whack the dead body all the way from the 3rd tower to the hidden loading point. If Tilt is turned off, you can also melee/destroy the Plasma Cannon support platform on the Separatist Phantom at the third tower. This will allow you to attain a weaponless Elite, who you can bring on a Mongoose.

If Thunderstorm is turned off, make sure at least five Deployable Covers are available and deploy four where the Carrier Forms spawn (two on both sides). Make it so that you can jump over them, but that it will simultaneously block the Carrier Forms from leaving the tower. Then hold on to one Deployable Cover and enter the third tower, activate the elevator, and get the Flood to spawn. Now run past the Flood and get to the entrance of the third tower. Use your Deployable Cover to block the Arbiter and then use a BR or Fuel Rod Gun to kill the combat forms (there should be at least three human combat forms and a few brute combat forms). Then just jump over the deployable covers, go down to the Phantom, and get the Elite on the turret off by meleeing the support platform. Finally, headshot all your marines and go to the waypoint. You should get a checkpoint. From this point on, it should be much more easier.

Explanation
The Flood Brute may be an old version of combat forms created in-game. The Flood would not totally change the host's body immediately after infection. This idea was cut from the game, possibly because the combat forms looked too similar to the original enemy. In addition, the combat forms would have been very formidable and intelligent enemies, and on Flood levels, would have been overwhelmingly powerful. The glitch occurs on The Covenant because there is a hidden loading point which removes all of the Flood from the level. When an Infection Form is in the process of transforming the dead Brute into a combat form and the player triggers the loading point, the Flood Infection Form is removed from the level, but ultimately resurrects the Brute, albeit his AI allegiance has been changed from the Covenant to the Gravemind.