Can somebody explain Pokerus to me? ^-^

[Dragonstrike]

- It permanently gives the pokemon double EV gains, even after it's 'cured'.  This stacks with (and doubles) the effect of power items.

Can you elaborate on this? For example, assuming we are talking about the same thing (correct me if I'm wrong,) what happens if I've already EV trained a pokemon to its max 252 with berries ect. What is being gained?

If a stat already has 255 (not 252, 255.  252 is only the max if using the Ninjas' punching bag minigame to maximize the stat) EVs in it (or if the pokemon has all 510 evs accumulated) and would gain more evs from defeating a pokemon, nothing happens.  No evs are gained if the pokemon is EV trained fully.

The part I'm talking about with this is the process of gaining EVs, and it's the main reason you want Pokerus in the first place.  If a pokemon that's been infected/'cured' of pokerus beats a pokemon, they gain double the EVs they normally would.  If they beat a Chyinmunk, for example, they would gain 2 Defense EVs instead of 1 (1*2=2).  If they beat a Chyinmunk while holding a Macho Brace, they'd gain 4 EVs instead of 1 (1*2*2=4).  And if they beat a Chyinmunk while holding a Power item, they'd gain 2 Def evs and 8 evs in the stat the power item is boosting for a total of 10 evs instead of the 1 Def and 4 from the Power item for a total of 5 EVs. (1*2 + 4*2 = 10)

Basically, it halves the time needed to fully EV train a pokemon.  (though it should also be noted that Pokerus has 0 effect on the results of the Ninjas' punching bag minigame)