Whats is pokerus?

Pokerus is an Pokemon Virus which doesn't effect them, well it does by increasing it's stats much fast than usual making it stronger and more effective in battle. Pokerus goes away in a few days but if you keep it in the PC it will stay on the pokemon. You can spread it to other Pokemon by having it in your party and it will eventually spread throughout all the Pokemon in your party. I hope you have fun with the pokerus. I am glad to help out. ~Twilight_Sasuke~

Pokerus is a virus that your Pokemon can get. It's a good thing though, as it means that your Mewtwo will level up faster. Pokerus actually helps your Pokemon level up. I think that if you put your Mewtwo in the PC, then the virus will spread to other Pokemon.

I'm not sure about that though, so you should ask an expert. One more experty than me I mean.

The Pokemon Virus, known as PokeRus, is a good "infection" to have.

It's pretty simple that's hard to explain, so to people who don't understand it won't have a clue to what I'm saying at first. But once I give you scenario, you'll probably understand it better.

Okay, let's talk about how PokeRus works first, before we go on explaining what it does. PokeRus spreads to the rest of your team if you walk around with your team a bit (just remember to have the Pokemon with PokeRus in your team; in this case, Mewtwo). PokeRus DOES indeed go away; so take advantage of this chance. In order to keep PokeRus on your Pokemon, just store them in your PC, and they'll keep it forever, so long as they're contained in there.

Now, what does PokeRus actually do?
Well, while your Pokemon has PokeRus, it's very easy for their stats to increase. However, one stat increases, one at a time. This is also a time when a Pokemon could change their EV.
First, when a Pokemon who has PokeRus gains a level, you might notice that one of their stats has had an abnormal increase compared to the increase of the other stats. This is what I was talking about.
When the Pokemon gains another level, a different stat might have gone up a lot.

For example, you have a level 50 Mewtwo. You level him up one level, and his HP goes up by 5 or 6 points, whereas the rest of his stats go up by 2 or 3 points. You raise him up another level, and this time, his Speed goes up by 5 or 6 points. Then, his Defense goes up by 5 or 6 points.
Note that using Rare Candies will NOT work.

And it just goes like that. Note that doing the above is known as "EV Training".

You are so lucky to have a mewtwo with pokerus!!! I wish I had that pokemon! Any way pokerus is a virus, it affects your Pokemon in a good way not in a bad way. Say you have a level 40 Mew your stats rise abnormally; way way way more than other pokemon. Your stats go up by about 5 or 6 points each time rather than 1 or 2 points each time.