From Halopedia, the Halo wiki

A Flood Hellion  as depicted in the Halo Encyclopedia (2022 edition).
General overview


Can vary its shape to counter enemy defenses. Can shelter large numbers of smaller Flood forms.

Method of attack:

Uses its flesh and bone as a living weapon


The Hellion is a variation of Flood pure form that serves as a mobile hive and siege machine.[1]


Hellions are a variation of pure form that are utilized by the Flood as a mobile hive and siege machine. Vaguely reflecting the majesty of the Gravemind, Hellions are able to incubate and shelter massive numbers of smaller parasites. They are formed in order to overwhelm even the most dedicated and stalwart planetary holdouts. Hellions possess the ability to alter their form in order to attack any defenses attempting to stop the Flood's unyielding spread, rending and refashioning their flesh and bone into a living weapon to assault their foes.[1]