Zombie Repeller Achievement in Halo: The Master Chief Collection

The Flood is a unique species of highly virulent parasitic organisms that reproduce by consuming sentient life forms that hold enough biomass and cognitive capability to sustain life. Argued to be the very sole reason why the entire events of the Halo Universe exist, the Flood are by far the greatest threat in the existence of life.

These enemies are extremely adaptable, dangerous, and expendable. Rarely will you ever encounter a firefight with the Flood in which victory will be smoothly achieved. There are a few different variants, ranging from the Infection form to the Carrier and Combat forms as well. The latter of the three – the Combat form – are the most vicious in battle.

Armed with nearly every type of weapon imaginable, you will be hard pressed to hold your own without arming yourself with significant firepower. Generally, the Shotgun and Energy Sword are the best weapons to use against the Flood. It is also important to take note of one peculiar note: When you kill a Combat form, they aren’t truly dead yet, because the Infection form can essentially “revive” them. With this said, make sure to shoot off – or slice off – their arms and heads and feet when they topple over to their assumed death.

Lastly, take note that the Flood does not appear until mid-game in Halo: Combat Evolved, Halo 2, and Halo 3. Specifically, they are present - in heavy force - in all Halo: CE missions after "343 Guilty Spark." In Halo 2, they are present in "The Oracle," "Sacred Icon," "Quarantine Zone," and "High Charity." Lastly, in Halo 3, they will appear in "Floodgate," "The Covenant," "Cortana," and "Halo." Furthermore, the Flood do not appear in Halo 4 at any time. Once you have killed a total of 1,000 Flood enemies, this achievement will unlock.