Rex
From Halopedia, the Halo wiki
Rex is an easter egg that has appeared in Halo: Combat Evolved, Halo 2, and Halo 3. The egg takes the form of the word "Rex" written on a level's scenery. It was added by Bungie programmer Tyson Green.
Halo: Combat Evolved Rex
The Maw
The word "Rex" can be found in the level The Maw, written on a wall in blood.
- Proceed normally through The Maw on any difficulty level, until you get to the huge Warthog jump/free fall.
- At the ledge, drive the Warthog to the right, so you land on the side of the floating platform.
- Enter the corridor and look to the right side. Spelled out in blood is the word Rex; on the other side, there is a bloody swastika.
Halo 2 Rex
Outskirts
On Outskirts, the word Rex is spelled in rocks with a pool of blood and a Covenant Energy Sword is sticking out of the ground.
- Get to the the rooftops and go to the area where the Jackal Snipers and Drones are.
- Keep going until you reach the building with two snipers in it.
- Turn and there should be a room in a building you can jump into, the Rex is in there, along with the sword. Keep in mind though that the Rex is not always in there and when it's not, the sword may not have infinite energy. Also, Rex does not appear in Co-op.
Great Journey
On top of the final tower in the Great Journey, the word "REX" is written in Flood blood. It seems that the only way to see this particular Rex is by using Dev Cam mode, unless you have a pile of Plasma Grenades, a Ghost, and you have the Sputnik Skull turned on. A video of how to get it can be found here.
The Arbiter
In The Arbiter, the word "Rex" is written in blood on the first column in the third room/hall, after the room with the Seraph. Simply proceed normally, killing all enemies near the Seraph, in the following hallway, and then in the room after that. Once done, go to the door; directly in front of you, there should be a column with "Rex" written on it.
