Named for its size and its power, the Flood Juggernaut is very large, about twice as tall as John-117 and the Elites. Its mighty tentacles can kill most enemies in a single strike. There is nothing left of any host in this form, other than the raw materials. Even the calcium has been broken down to function as natural armor.
The Juggernaut has two extremely large tentacles that can kill the player with only one hit. Some have spikes on their tentacles. They also can jump much higher and farther than the regular Combat Forms can. "Modders" and Halo 2 Vista users can fight against the Juggernaut on the level High Charity, by switching them to spawn in place of another character's existing spawn point.
They often jump extremely high in the air at the player when noticed, sometimes landing on players, instantly killing them. The Juggernaut will also sometimes forget the player is there, and just stand still for a few moments. Finding cover is ill-advised, as the Juggernaut will usually hit it out of the way, sending the object an extreme distance. One of the best tactics is to run to the Pelican and get inside of it, since the Juggernauts are too tall to follow in, it will wait until the player exits the vehicle.
There would never be more than one Juggernaut in any given place. Once the player eliminated it, the combat forms that were supplementing it would go "offline." The Juggernaut has four to six infection forms inside its body to control it, similar to Combat Forms. It was supposed to be "this uber-intelligent mini boss, but the suggested intelligence was way too high for what design needed to use it for, which was as a big tank."
The Juggernaut appears to be very tough, resisting almost anything and making its death even harder to achieve, possibly making it go berserk. If the player has picked up the Shotgun and/or Rocket launcher he/she can make things easier. If not, they will have to rely on sticking them with grenades and attacking with whatever weapons available.
Through modding, it has also been found that the Juggernauts have a defensive position; stopping and moving their whip-like appendages in front of their body in an X formation. It is unknown why such a powerful creature needs such a stance. It could possibly be to counter the sword or merely for looks. It may also be a taunt to lure players in. Note, that it looks like the defensive position of Hunters, although it is confirmed that the Juggernauts are not transformed from Hunters, as Hunters are immune to the Flood due to lacking a single central nervous system.
When running low on health, some occurrences have happened where the Juggernaut goes berserk, waving its tentacles around wildly before striking the player with speed.
The Juggernaut was created for Sacred Icon and Quarantine Zone as a way to stop the Enforcers, and one can imagine that with its long legs and tentacles that it would have little problem snatching an Enforcer out of the sky and tearing it apart. The Flood Juggernaut can leap twice as far as the already impressive jumping capability of a Combat Form, and it has the power of a tank.
Juggernauts were also slated to appear in the level The Oracle. Additionally, although the model, textures, etc., are stored in the files for High Charity, there are no Spawn Points meant for it. As Bungie never programmed a death animation for the Juggernaut, when it runs out of health, it will just freeze in place.
Code within the files for the levels The Oracle, Sacred Icon and Quarantine Zone indicates these missions were to have had Juggernaut spawns within them, though the level files themselves do not contain the Juggernaut assets. The Oracle would have one Juggernaut hidden in the fog (not able to be fought), and one attacking the Flood research laboratory later on in the mission. Another would spawn in the defense section near the end of Sacred Icon, while six were to spawn on Quarantine Zone - likely due to the abundance of heavy vehicles in the mission. These Juggernauts would have spawned as follows; two in the canyon in front of the destroyed Sentinel manufacturing facility, one inside, one outside the exit and two more at the entrance to the gondola.
- The Juggernaut originally was only found within the game files of Halo 2, similar to the Huragok in Halo: Combat Evolved, and hadn't been featured in any other title until it was mentioned in Halo Wars 2's Phoenix Logs and eventually its first physical appearance in the new Halo: Fireteam Raven arcade rail shooter game.
- The Halo: Fireteam Raven Flood Juggernaut appears to be the same as the Halo 2 version of the enemy, aside from the new animation overhauls
- The original Flood Juggernaut had most of its animations at least partially complete, aside from the death animation, which has finally been added. The creature acts very similarly to the Carrier form, in which it explodes into multiple pieces upon getting its long tentacles seperated. After the arms are seperated, the Juggernaut gets disoriented and flails in place as if it was losing its balance.
- The Flood Juggernaut along with the Tank form were never seen in the original Combat Evolved, as they hadn't been created for any game at that time. However, according to the game's lore, it is possible they were speciments left in the research laboratories of the Installation 04, dating back to the Forerunner-Flood war. It is unclear as to why they only attacked the ODSTs in Fireteam Raven and never were encountered by 117 in the original game.
- If the Juggernaut had been included in Halo 2, you would have had to fight against eight Juggernauts.
- The Juggernaut may be an unseen Flood form, but it actually exists. It was mentioned in the Flood Autopsy article on Bungie.net, where it was categorized as an "Advanced Form" along with the Gravemind.
- Juggernauts are playable pieces in Halo Wars Risk. But they do not resemble the Juggernaut, rather looking like a Thrasher Form instead.
- In the former Feast of Bones article on Bungie.net, Robert McLees mentions additional details about the Juggernaut.
- In the book The Art of Halo there is a concept sketch of the Flood Carrier Form that looks just like the Juggernaut.
- In the level The Oracle, the first chapter's name is Juggernaut. It is possible that the Flood Juggernaut was originally going to be introduced into this chapter of the level as there are script files in the map.
- The Pure Forms seen in Halo 3 are inspired by the Flood Juggernaut. The Abomination in Halo Wars 2 also appears to be based on the appearance of the Juggernaut.