Secret Marine on The Covenant

The Secret Marine on The Covenant can be found, as one might expect, in Halo 3 's Campaign level The Covenant. As one might also expect, the supposed Easter Egg takes the form of a Marine hidden in a hard-to-access location.

The Marine only appears on single-player Local Play, and can be accessed using a Ghost or a Prowler. Sometimes, two or more Marines will appear. It is suspected that the faster you get to the Marine, the more Marines you will find. There appears to be a kind of "time limit", after which the Marine will not be present -- whether he disappears or heads to another location is unknown. Once you encounter him, though, he will never leave his position.

Instructions
300px|right

Ghost
Start at Rally Point Bravo. Grab a Mongoose and drive straight ahead at full speed. When you get to the part where a Marine says, "Citadel in sight". Get off of your Mongoose and grab a Ghost as soon as possible. Drive the Ghost ahead as normal. When you approach a tunnel, turn right and climb straight up the mountain. There, you will find the Marine(s).

Prowler
You can also do this in a Prowler - steal one from the Brutes in the area before the tunnel. Once you get to the ridge on the top, you will need to pick your path carefully -- some parts of the final ascent are too steep for a Prowler. Also, the Prowler is very slow, so you may reach the top only to find that the Marine has vanished.