Flood pure form

Pure Form is a new type of Flood that is featured in Halo 3. There are three sub forms, the Stalker Form, Ranged Form, and the Tank Form. Each Pure Form can mutate into another, with the Stalker seeming to be the "base organism" that the other two forms mutate from. As implied by its name, Pure Forms are not products of a biological host, but are instead conceived entirely of the Flood like the small Infection Forms. As such, that they are also different from their parasite-ridden counterparts in that they are not made out of weak, rotting flesh, but a hardened carapace of of recycled/recompiled bones and biomass that you cannot dismember or "sterilize" like you can with the parasitic Combat Forms, even with weapons as powerful as the Flamethrower. However, once you do kill them, they do not come back, much like non-flood enemies.