When I was trading online I got a shiny darkrai for a entei but when I..

Otherwise known as PokeRus, while you train this Pokemon and level him up without using Rare Candies, his stats raise abnormally fast, and this is to change the pokemon's EV, also known as EV Training. Trainers typically EV train their Pokemon when they want Hidden Power to be a specific type.

If you want your Pokemon to keep it forever, store them in the PC. Although they won't be getting anywhere, they'll still have it.

If you want to spread the PokeRus throughout your team, you have to walk with your team that has at least one Pokemon with PokeRus. I'm not sure how long it takes, I only know that fact :]

This used to be thought of as Pokemon fokelore! An urban myth, if you like. But it seems it really exists!

Allegedly, it's a good thing! I've never encountered this myself, but I've heard a lot of evidence to suggest that it happens when you only use one Pokemon a exclusively in all your battles for a long time. either that or you encounter a sick wild Pokemon, or you catch a sick, wild Pokemon and put it in your party.

When your Pokemon has the virus (pokerus) it can spread to the other members in your Pokemon party. This is also meant to be a good thing, because it's meant to make them really strong, powerful. And by spreading the virus, you make it last longer. (this is all anecdotal evidence, though, I'm unsure of it's validity)

But, apparently if you just leave it, it will go away.

It just makes your Pokemon exp go up faster or thats what I got told by the game sorry if I was wrong

It raises your pokemons stats more when it levels up.

The pokevirus is a very rare and could thing

The pokvirus or pokerus as it is named will raise the stats of your Pokemon faster that a normall non infected pokmone will and it will he will be cured of it in like a month and once he is cured he can never get it again you can tell if he has been cured if he has a smiley face next to his sprite pic when you look at his summarry

It will infect your other Pokemon the more you battle with them as long as darkrai is in your party and he battles to

It has the infamous "Pokerus". It helps your Pokemon grow faster.

-Shadow Cresselia