Pokérus
 

Bit surprised I searched around this forum a bit and couldn't find any other threads on this.

For those of you who don't know, it's basically an infection that Pokémon can get that causes them to gain double effort values in battle. Odds of running into it in the wild are something like a sixth of the Gen 6 Shiny chance, but it can be spread between Pokémon during battle.

You can also trade it to people, and a few hours ago I discovered six or seven infected Pokémon in a Gen 5 box, transferred them to AS and spent a good part of the last few hours spreading it around the rest of all of the Pokémon I have. Anyone want some? Good for EV training in the wild, if you're not much of a Super Training person.

Nah, I don't have much interest in it, but it's incredibly easy to get now, especially when folks have been distributing it over Wonder Trade since X and Y were released.

Fair enough. Also I've somehow never heard of that before, might set some of it free on Wonder Trade myself later on.