Orpheus

Orpheus is a Halo 3 Meta-Game Achievement. It is unlocked when the player earns 15,000 points while playing the meta-game on Cortana. This Achievement awards the player 10 Gamerpoints.

It is represented by a blue circle, with a fist and lightning bolts in it.

The name Orpheus is most likely a reference to the Greek myth of Orpheus, a man who entered the underworld to rescue his wife, just as Master Chief entered the "underworld" of the Flood-infested High Charity to rescue Cortana.

Methods
Method 1

On Normal, activate the Tough Luck, Catch, Fog, and Famine Skulls because for the Tough Luck and Catch, they don't dodge or throw grenades. It would be a good idea to use a Shotgun/Energy Sword in combination with a Battle Rifle/Carbine. Also, try to get as many medals as you can -- for example, grenade sticks or headshots. Headshots can be obtained by firing a headshot-capable weapon, such as the Battle Rifle, at the feeder tendrils on a Flood Combat Form's chest; this kills the Infection Form controlling the body.

Note: When trying to get the Meta-Game Achievements for any level containing the Flood, kill as many Combat Forms as possible with weapons that do not destroy the Combat Form's body. Once the area is clear, back up and let the Infection Forms resurrect the fallen Flood. Kill all the Combat Forms again to gain more points. If no Infection Forms remain and there are blister-like sacs on the wall near you, pop them by shooting or meleeing them to release a small amount of Infection Forms.

Internal

 * Halo 3 Achievements
 * Cortana (Level)