Caeli Kingdom's Prisoners damned to severe punishments including death. To become a Bhopper, they had to be rabbits, promise serving their superiors(everyone in Caeli) and the Caeli Kingdom and pray to one of the Goddess Sisters(or both) to survive for their parole.

The Bhoppers were commonly used as mules, meatshields if they disobey or fail orders, scouting groups, mailmen and sex slaves, and they had no permission to wear metal-plated nor chainmailed armor, limiting them to wear their prisoner clothing and leather or padded armor to survive, a thing that is pretty good for them because they're the most lightweight and agile special force the Caeli Kingdom has to fight the other factions and their other special forces. Bhoppers rarely survived, but if they survive, they are rewarded with goods and the permission to be pardoned from crimes.Maybe...

This special force may be the weakest they fought in the War of Elements in appearance, but in battles, like a Caeli soldier, they are skillful with their airbending skills and various weapons, but they can't equip explosives unless if used as a meat cannon or if it's very important for them to grab them.

After the War of Elements ended, The Caeli Kingdom has been overthrown and this special force wasn't needed anymore and has been disbanded. The fate of the former remaining Bhoppers remained unknown.

Ninjas were originally big groups of civilians who voluntarily joined to serve the Aqua Empire because they have a rivalry against the Earth Snakes because they can easily cure their venom with their water arts and they're very skillful combatants.

Their authority level isn't the big deal, they originally were civilians in the Aqua Empire's eyes, and that annoyed the Aqua Emperor, so he offered all of them to work for the Aqua Empire and all of the ninjas accepted.

They rarely move out of their comfort zone that is the areas they control, because they're expert defenders. However, the Ninjas prefer to carry lightweight equipment for their missions.

When the War of Elemets ended, various Ninjas abandoned the Aqua Empire to return to their clans.

Rock Snakes are heartless and greedy assassins and mercenaries who somehow, got hired to serve Terra.

The majority of their members would enjoy to steal goods from the royals or were craving to stab their customers from behind when they had the chance to do it, but being very well paid for sabotaging rival factions and murder important persons from rival factions was more profitable and funnier for them.

Their Authority level is based of their customer's job, but they never got hired to be a commanding job higher than a subliutenant or sergeant if their customer is a militar to prevent giving these merciless thiefs more power and liberty than a common soldier.

Their weaponry is full of poison, that's why they have that name as a "special force" and they rivalize with the Aqua Ninjas because their waterbending is very useful to clear out their toxins from their victims they try to murder.

When the War of Elements ended, this "special force", instead of be disbanded like the other three special forces, the Supreme Lord Terra took the chance of arrest and execute the majority of the snakes he was able to find before they were able to react quickly or betray the Terra Authorities. The fate of the remaining criminal guild's members remained unknown, but the Supreme Lord Terra won't hesitate in governing with a solid hand and punish everyone in the Terra Continent who dares to be a menace for his Faction or whoever dares to challenge his authority and power.

Ignis' Hellhounds were the opposite of those rabbit weaklings who call themselves "Bhoppers", The Hellhounds Squadron was created by and for the war, they were brave soldiers who didn't fear to charge against batallions of enemy soldiers beause their enemies were the ones who must have been scared of their existence.

The Hellhounds were very well sustained by the Ignis Emperors, had a better treatment than a general and they were able to do anything to serve their faction. Of course their authority level was above General, commonly mentioned as the "TRUE General Rank".

The rank application to become a Hellhound was a scary mistery for several Ignis militars, specially, for those who were interested to join to this legendary special force, it was known that only the current Hellhounds can choose by voting, their next new members if one or multiple of them were MIA(Missing In Action) or KIA(Killed in Action) and the potentially next Hellhound member had to be a canine and to be a godlike with the firebending.

When the War of Elements ended, the Hellhounds' remaining members needed to disband this hellish rank to cry for their fallen buddies and rest their war wounds and scars in deserved vacations or in a asylum like the rest of veterans suffering from PTSD.