The time has come again for the online Pokemon International Challenge, and this year it's taking place in May. Registration will begin on May 8th, and will feature 50,000 participants at its cap -- so sign up soon! The actual event is from May 16th to the 18th. Typical rules apply, like double battles only, and only Kalos Pokemon (nothing transported).
Sounds simple enough!
Pokémon Announces 2014 International Challenge May [Nintendo Life]