The Pillar Form is one of the Flood pure forms that evolves from the Dart Form. Once a single Dart has absorbed a critical amount of Flood biomass, it morphs in to the Pillar Form.
Taking down a Pillar Form is not easy. The inside has been found to be hollow, and attacking the outer skin is often ineffective, as the Pillar Form has an incredible ability to heal. There is a central brain that controls the giant creature from the inside. Its destruction will cause the creature to die and collapse, unless the Pillar has anchored itself to the ceiling.
The Pillar's height is variable, ranging from just a few meters to hundreds. Its surface is like most Flood forms, a mottled brown and gray. Tentacles sprout from random intervals, and organic blades spring from the tip. These blades have been known to shred MJOLNIR Mk. VII armor right after they punch through the shields.