Rex

"rex" spelled in blood in Halo: Combat Evolved.

Rex is an Easter egg that has appeared in Halo: Combat Evolved and Halo 2. The egg takes the form of the word "Rex" written on a level's scenery. It was added by Bungie programmer Tyson Green as a reference to his username "Ferrex".

Halo: Combat Evolved

The Maw

The word "Rex" can be found in the level The Maw, written on a wall in blood.

1. Proceed normally through The Maw on any difficulty level, until you get to the huge Warthog jump/free fall.
2. At the ledge, drive the Warthog to the right, so you land on the side of the floating platform.
3. Enter the corridor and look to the right side. Spelled out in blood is the word Rex.

Halo 2

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. In Halo 2: Anniversary's remastered graphics mode, Rex is spelled out in shotgun shells.

1. Get to the rooftops and go to the area where the Jackal Snipers and Drones are.
2. Keep going until you reach the building with two snipers in it.
3. 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 is, the sword may not have infinite energy. Rex does not appear in Co-op.

The Great Journey

On top of the control room on The Great Journey, the word "REX" is written in Flood blood. To reach the text in-game though, there are a few methods:

1. Dev Cam mode.
2. By launching a Karo'etba-pattern Ghost with a pile of Anskum-pattern plasma grenades with the Sputnik Skull turned on. A video of how to perform this trick can be found here.
3. Flying to the top of the control room with the Acrophobia Skull added to Halo: The Master Chief Collection. The text is only visible in the Classic graphics mode.

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  "REX" spelled in rocks in Halo 2.

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  "REX" spelled in shotgun shells in Halo 2: Anniversary.

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  "REX" spelled in blood on Halo 2's The Great Journey.

REX spelled in blood on Halo 2's "The Great Journey".

Trivia

In Halo: The Master Chief Collection, finding the Rex text on The Maw will unlock the T-Rex achievement, while finding the Rex Sword in Outskirts will unlock the Rex Sword achievement.