What is Pokérus?
Pokérus, is a Pokémon virus, and combined this makes the word Pokérus. Pokémon-virus Poké + rus. Now this disease helps the Pokémon that has it grow faster. However, it doesn't gain experience faster, it gains EVs faster. It actually doubles the EVs, so lets say that...
Empoleon-Pokérus fights a Gastly. Of course the Empoleon would gain experience just like normal, but then the EV gain would be doubled. So instead of getting one special attack EV you would get 2 EVs towards special attack. It's really a nice thing to have in training, you could have an awesome level 50 Pokémon that could take down Pokémon that out level you.
Where and how do you get Pokérus?
There is no specific place that you can get Pokérus, you can get Pokérus from wild Pokémon. You could either luckily catch a Pokémon with Pokérus and then spread it to the rest of your party. If you battle a wild Pokémon that has pokerus, odds are that you are going to get it. You won't know if the wild Pokémon has it until you actually get it. The odds are just a little bit better then encountering a shiny Pokémon. Basically, the odds are not very good.
How do I know if I have Pokérus?
This is easy, all you have to do is click on your Pokémon's summary and then look up in the top-right corner of your Pokémon's picture and see if there is a purple block there, if there is then on that block should be the letters PKRS Pokérus just abbreviated.
Also, if a Pokémon already has Pokérus then there should a smiley face by their picture.
What if my Pokémon already has Pokérus but it has a smiley face?
In that case then you can no longer spread the disease using that Pokémon. The effects of Pokérus are still working, it just is no longer contagious.
How do I spread Pokérus?
This is quite simple. I made up a way to do this effectively.
Member 1: Pokérus: Member 2: Member 3: Member 4: Member 5: Member 6:
So Member 1 has Pokérus have it battle a few times then member 2 should get it which is perfect. Once member 2 has it then switch member 2 and member three around so it will look like this
Member 1: Pokérus: Member 3: Member 2: Pokérus: Member 4: Member 5: member 6:
Then battle some more and when member 3 gets Pokérus member 4 will too. So then you switch member 3 and member 5.
Member 1: Pokérus: Member 5 Member 2: Pokérus: Member 4: Pokérus Member 3: Pokérus: Member 6:
Then battle a few more times and all of the Pokémon should have Pokérus in your party. Be warned at midnight any Pokémon with Pokérus in your party will be cured at midnight. If the Pokémon is in your PC, it wont be cured. To keep Pokémon uncured, put them into your party before midnight so they can continue spreading the virus to other Pokémon.
This technique was also posted in the EV guide part of the wiki.
When does Pokérus stop being contagious?
When it's been in your party for 24 hours. Alternatively, it will naturally cure if it's in your party at midnight.
Is Pokérus something I want to have?
Just in case you missed this, the answer is yes. If you thought it was a bad thing then read through the guide again.