To win, the survivors must survive for the specified amount of time while the Flood must infect the survivors. Survivors are equipped with a Shotgun and Magnum by default while the Flood will use their claw to melee the enemy. Both the survivors and the Flood have their own sets of loadouts to choose from. Each loadout is differentiated by an Armor Ability by default.
- Compared to Spartans, Flood move faster (however they cannot sprint), react differently to bullets, and have specially-tuned armor abilities.
- The Flood have a unique character model for both first and third-person.
- A special mist effect trails behind Flood characters.
- A first-person screen effect shows the haunted view of a Flood.
- When playing as the Flood or Last Man Standing, music plays in the background to intensify the experience.
- A specific sound effect accompanies the Flood which sounds like a squishing/dripping sound combined with the sound of an Infection Form.
- Flood Conversion: Convert a Spartan to the Flood
- Alpha Conversion: Convert a Spartan to the Flood as an Alpha
- Infector: Kill 2 Spartans in a row as a Flood without dying
- Carrier: Kill 3 Spartans in a row as a Flood without dying
- Juggernaut: Kill 4 Spartans in a row as a Flood without dying
- Gravemind: Kill ALL Spartans in a row as a Flood without dying
- Flood Kill: Kill a Flood
- Flood Kill Assist: Assist killing a Flood
- Flood Hunter: Kill 4 Flood in a row as a Spartan without dying
- Flood Survivor: Kill 6 Flood in a row as a Spartan without dying
- Flood Exterminator: Kill 10 Flood in a row as a Spartan without dying
- Last Man Standing: Be the last surviving Spartan
- Final Conversion: Kill the last remaining Spartan
- Flood Victory: Contribute to the Flood total conversion of all Spartans
- Ancient One: Survive the entire round as a Flood and convert at least one Spartan
- Clever: Survive the entire round as a Spartan
- The Flood forms have a few traits that set them apart from regular Flood Combat Forms: they lack the sensory tentacles of most combat forms, the host's head is still intact (and highly modified), and their melee weapon is a claw as opposed to tentacles and on the right arm as opposed to the left.
- The Flood appear to be wearing the bodysuits of the GEN II Mjolnir armor, but not the armor itself.