Instructions
Travel to Pokemon Battle Revolution in order to capture Electrive. Go to "Self Introduction" in your profile and enter the code BA16-X4SH-EZAT. Visit the shop in Mystery Gift and it will transfer to your DS.
Unlock the Mystery Gift by going to the Jubilife TV and talking to the man. Tell him "EVERYONE" (or sometimes) "EVERYBODY" happy and then say "WI-FI" connection.
Capture Leafeon by leveling up your Eevee near Moss Rock near the Externa Forest exit. To capture Glaceon, level the Eevee up near Ice Rock, which is on the way to Snowpoint City.
Visit Verity Lakefront to catch Mesprit. When you approach Mesprit, it will run away, so you'll need to track it with the Poketch app. Try to hurt it just once, then let it go. Do this until its HP is in the red zone, then you can catch it with a quick ball.
Get an Eevee from Bebe once you have the National Pokedex. You must collect an opposite gender Eevee from your GBA or Trophy Garden in order to mate. Put them in couples day care in Solaceon Town. They'll produce an egg, which you can hatch for a new Eevee.