A Few General EV Training Tips:
Pokérus doubles the EVs gained per Pokémon defeated.
Macho Brace doubles the EVs gained per Pokémon defeated.
Power items add +4 in a specific stat to the EVs gained per Pokémon defeated.
With Exp. Share ON, all Pokémon in the party gain EVs.
A Few Horde EV Training Tips:
Using Sweet Scent or Honey initiates a Horde battle 100% of the time on the routes listed below.
Common Sweet Scent Pokémon include Combee (Route 4) and Bulbasaur (Pokémon Lab).
Horde battles will not activate on rainy routes.
If it is currently raining on a route you were going to use for EV training, choose another route from the list below.
To defeat all five Pokémon in one turn, use a powerful Pokémon with a move that hits all opponents.
Common choices include Pokémon with Surf, Parabolic Charge Heliolisk, and Petal Blizzard Venusaur.
You gain EVs for each Pokémon defeated in battle. In Horde battles, you gain a total of five times the regular EVs.
Power item, Macho Brace, and Pokérus boosts are applied to each Pokémon defeated.
With Exp. Share ON, a Pokémon who does not participate in battle can gain additional EVs by equipping the aforementioned EV-boosting items.
An Explanation of Horde EV Math:
The total number of EVs gained from defeating every Pokémon in a Horde Battle can be found at the end of each line below.
Pokérus doubles the total EV gain per Horde Battle.
Macho Brace doubles the total EV gain per Horde Battle.
Power Items add four EVs per Pokémon defeated.
All multipliers are cumulative (e.g., Pokérus + Macho Brace = 4*EVs).
Most Efficient Routes for EV Training
These routes take into account frequency of encounters, number of EVs gained per Pokémon defeated, and ease of access to the location.
HP - Route 5, Connecting Cave, Route 20
Attack - Route 19, Route 14
Defense - Terminus Cave, Victory Road
Special Attack - Frost Cavern
Special Defense - Reflection Cave
Speed - Route 8, Route 12, Route 15