Flying Rtas 'Vadum
From Halopedia, the Halo wiki
On the level The Oracle kill all of your allies at the very beginning except Half-Jaw. Then, go to the next room, kill the Flood Combat Forms and trigger the Holo-Drone. Right after it disappears take out Half-Jaw's shield and lure the Flood Infection Forms to him. As more infection forms attack him he will begin to rise off the ground and sometimes fly straight up.
