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. The Juggernaut was created for 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 originally slated to appear in the levels The Oracle and Quarantine Zone. Although the model, textures, etc., are stored in the files of High Charity, there are no Spawn Points meant for it. As Bungie never programmed a death animation for the Juggernaut, when it "dies", it will just freeze in place.
The Flood Juggernaut was the progenitor of the Pure Forms seen in Halo 3. 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. Whereas the earlier Combat Forms were hosts used as vehicles, with the Pure Forms, the host material is used as building blocks to craft the ultimate form.
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 further 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 Form is not featured in any Halo game, but it is embedded in the Halo 2 programming and can be found via modding, similar to the Huragok in Halo: Combat Evolved.
- If the Juggernaut had been included in Halo 2, you would only have had to fight two Juggernauts in the whole game.
- 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 Bonesarticle 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 Flood Tank Form in Halo 3 may have been inspired by the Juggernaut, as they do the same thing, just that the Tank form is much smaller and weaker.
- This also may be true with the Thrasher form in Halo Wars.