Pokerus / Hypersation Virus (HSV)

This is indicated on a Pokemon by this marker (👾).

The Hypersation Virus, more commonly known as the HSV or the Pokérus, is an incredibly rare virus only found in certain dungeons near the Heart of Kogranar. It was first discovered at an area nicknamed the "Arena of Desire" which ruins were found near the Field of Sin for the longest time. It is a virus known to be incredibly contagious, spreading by being present near an infected Pokémon for extended periods of time, though in mostly mysterious ways. It would, then, vanish in ways as mysterious as how it would appear.

Symptoms mainly manifests in the form of emotions, feelings & desires amplifying in ways most Pokémon would not be able to control themselves. It often causes those affected to feel they can do anything with the boost of abilities (whether in battle or in general) to the point their sense of moderation are either dulled or completely gone during the time of infection. Many describe those infected by Pokérus as zombies, only using their own emotions & desires as drive to do anything, which also causes them to no longer use any judgement.  

There are no ways of healing from this but to wait the effects out, which can take a few days to over 2 weeks. This period is considered to be the infectuous state, which means a Pokémon can spread Pokérus during this phase. The duration of the symptoms often depends on a Pokémon's emotional intelligence / experience. Once healed, a Pokémon cannot be re-infected by Pokérus.

While normally Pokérus randomly appears and disappears, there has been secret work at the Heart of Kogranar which have been studying the Pokérus for years, using remaining samples found at the Arena of Desire shortly before it had been destroyed. This research intended of using the Pokérus' boost in abilities while trying to nullify the side-effects. However, the work was soon terminated due to the original participants of this research project being taken by Dungeon Madness.

THE POWER-UP PROJECT

With the Arena of Desire being near the Field of Sin & the entrance to the Heart of Kogranar, the Pokérus & the practices of the colosseum were still spread to those areas. It was incredibly difficult for those living near the arena not to know about the Pokérus & the battle-crazy Pokémon living there. This has caused a group of researchers who have been going to the surface from the Heart of Kogranar to look into the Pokérus and even spent countless sleepless nights in an attempt to swab a singular sample of the Pokérus.

Though, by sheer luck, they managed to get a minuscule sample, one that would require a microscope to even perceive. But, they knew they got it.

And so, with hard work, they separated the virus, studying each component very carefully. They, then, managed to figure out the part that was causing the infection: a tiny DNA fragment which orchestrated the entire thing. With this piece of the puzzle, the researchers attempted to isolate the part which gave the power-up while leaving behind the rest which was causing the involuntary amplification of emotions.

Unfortunately, when they thought they isolated the power-up and placed it in a brooch to conserve it and to eventually spread it to those in need... It was simply the entire virus. No matter what they did, no matter how much they cut from that piece of DNA, nothing worked. And, unfortunately, their project came to a halt as everyone participating were infected by Dungeon Madness in desperation from trying to find new technology around the Heart of Kogranar that would solve this mystery.

INTERACTIONS WITH DUNGEON MADNESS

While it is confirmed that Pokérus & Dungeon Madness are two completely separate things, it has been observed that due to Pokérus' ability to amplify emotions & physical abilities, it has a multiplicative ability on Dungeon Madness, not only making it more powerful and potent, but also causes a Pokémon with it to advance through the stages more quickly. A great majority of Pokémon with both ailments tend to be in later Dungeon Madness stages (Stage 3-4, usually 4) and tend to have barely any control, if at all. Only instinct and their own desire control their actions. Friends and foes no longer matter, as long as the desires are quenched... if even possible.

Some Pokémon with both ailments can match with Stage Finale Dungeon Madness in power even without Godly. A Pokémon with both Dungeon Madness and an infectuous state of Pokérus can spread BOTH ailments to Pokémon around them. This is a particularity of the combo, as Dungeon Madness usually is not transmissible.

When Pokérus no longer becomes contagious in a Dungeon Maddened Pokémon, they retain everything they have gained from it, but they won't typically remember what they have done while under the Pokérus. This is almost as if the heightened emotions hinders memory a lot as well.