Stalker Form

The Stalker Form is a Flood Pure Form that specialises in stealth and agility. It is apparently made from the recast bone of dead enemies. Upon heavy damage it will mutate into a Ranged Form or a Tank Form.

This form sits low beneath your field of view and their attacks can go widely unnoticed until you look down. They are able to crawl on walls and ceilings like a spider with relative ease and are capable of tremendous jumps much like the normal parasitic combat forms. A possible flaw in the Halo 3 AI is that it has been observed to rarely attack the player, and normally prefers to mutate itself into one of the two other Pure Forms.

Killing Stalker Forms
Stalker forms are weak but they are incredibly fast and agile. If you can get up close, a single melee attack from any weapon can usually bring one down. Any projectile weapon will do, but grenades do a better job much because their spindly physique makes them harder to hit. If you hit them with an Incendiary Grenade or a Flamethrower, they will instantly jump away and scream. Then they will die after a few seconds of burning.