There are often several different Horde Battles that you can fight to get the same EVs you’re looking for, but since they’re all only 60% encounters, that usually means 40% of the time you’ll run into something you need to run away from. That means each Horde Battle against five Pokémon that give 1 EV each results in an astonishing 50 EVs gained with both a Power Item and the Pokérus. Power Items particularly shine here, because they will give +4 to the EV gains for each Pokémon in the Horde Battle, which can then further be doubled if the Pokémon has the Pokérus. Because of this, you’ll want a strong Pokémon with a multi-target move and then you’ll want the Pokémon you’re EV Training to hold a Power Item for the stat you’re EV Training or a Macho Brace. Share and the Macho Brace or a Power Item, meaning you can have one high-level lead Pokémon that can EV Train all of the other Pokémon on your team without having to switch back and forth. Share, you no longer need to choose between the Exp. In addition to that, thanks to the changes of the Exp. You need a Pokémon in your party with Sweet Scent (Illumise, Weepinbell, and Masquerain are some examples of Pokémon that can learn it) and then you can use it as a field move from the party menu while standing in tall grass or in a cave to immediately summon a Horde Battle. Attacks that damage multiple Pokémon, like Surf, Earthquake, etc., will hit every Pokémon in a Horde Battle. In Horde Battles, you fight 5 wild Pokémon at once.
The thing that makes EV Training extremely fast in the Generation VI games is Horde Battles. It may seem like a good way to EV Train, but it’s far from the best way and goes quite slow in comparison to another newly-added feature that speeds up EV Training. Super Training is an option available on the PSS, which puts the whole process of EV Training into a minigame. Pokémon X & Y did a lot of things to help make the whole process of getting competitive Pokémon much easier and more streamlined, which means EV Training in X & Y is pretty straightforward.