Flood tank form

The Flood Tank Form is a type of Flood from Halo 3. It is a Pure Form, originally derived by mutating from the Stalker Form.

The Tank Form is similar in appearance to the Drinol (possibly inspired by the Drinol, who has never made it into any of the games), or a Hunter. Tank Forms are slow in comparison to the other Combat Forms but they make up for it with relative resilience and their devastating melee attack as they cannot pick up or use weapons with their arms that are shaped into hardened spikes (as opposed to whip-like tentacles exhibited by other Combat Forms). On occasion these large combat forms eject Infection Forms from their 'mouth' as if regurgitating them (not explosively like the Flood Carrier Forms and possibly only on harder difficulties) as a form of short ranged attack, or an attack to counter act bubbleshields. Like all of the Pure Forms, The Tank forms cannot be dismembered, only disabled.

Killing Tank Forms
The best way to take a tank form down is by shooting at the head/mouth which it often covers with one arm for protection. If you hit there with a projectile weapon (E. Battle Rifle) it will count as a headshot. All flood Combat forms has this "head mouth".

They are extremely tough, and attacks that destroy normal Combat forms with one hit deal far less damage to a tank form. They are able to take multiple hits from the Gravity Hammer and the Shotgun, but the Energy Sword seems to make shorter work of them- many times killing them in one hit. Since they are very slow and unable to rush the player, the Flamethrower or Firebombs are a simple, ranged, one-hit option against the Tank Forms. Brute-shots are extremely effective against them because its melee is an instant kill against them on all levels except legendary, which takes 1 shot and a hit. Plasma grenades are also very effective if placed near the head.

Trivia
Juggernaut, Flood Combat and Tank Forms have a "mouth like" head, where the sensory tentacles are