Horde Encounters are a feature that were first introduced in Pokémon X & Y. In these battles in the wild, you will face up against 5 wild Pokémon at the same time. This helps you build up a large amount of Experience Points and also aids in the training of Pokémon's Effort Values
Like before, Hordes can often provide all of the same species, and even sometimes introduce one Pokémon into the horde which is different to the others.
This game also introduces several areas where only one Pokémon will appear as a horde, making them perfect for EV training.
A new variation of the Horde Encounters is introduced in this game, however. In this game, you will sometimes be attacked by multiple trainer characters, such as a group of Team Aqua/Magma grunts at one time. These trainers will then send out five Pokémon to face you at a time. The mechanics work similar to before, with various moves being able to hit all Pokémon, so you need to plan ahead. There are only two instances of this in the game, but they employ strong strategies such as using 5 Mightyena, each with Intimidate and Snarl.