Guardian Forest is a level that was cut from the final version of Halo 3. The level would have introduced a new enemy called "The Guardian." At the end of the mission, the player would have had to battle a giant Sentinel similar to an Enforcer from Halo 2. Part of the level later became the multiplayer map Guardian, while another part (that involved a Hornet air battle) was transferred to the level The Covenant.
While developing the Halo games, Bungie, 343 Industries and Ensemble Studios have had to cut some content, such as vehicles, gameplay, and story elements, from the final products. Much of this content has been confirmed by videos and commentary in special edition DVDs, interviews with developers, and released concept art.