The Oracle

Summary
A Halo 2 campaign level, where the player plays as the Arbiter. Starting directly after you land the Banshee you were flying in the previous level, the opening cutscene has "Half-Jaw" comment on smelling a familiar stench.

This is the first level in Halo 2 where one encounters the Flood and some of their new abilities, most notably the ability of Infection Forms to revive fallen Combat Forms.

The player goes down an elevator and up to the top of the Gas Mine to cut three cables. He then must backtrack to the hangar of the previous structure, complete with another Banshee-flying section, where he engages in combat with the Heretic Leader to prevent him escaping Threshold in a Seraph. In the cutscene directly before the fight, it is shown that 343 Guilty Spark had survived the destruction of Installation 04 and was responsible for the "heresy" through his teachings.