Lopunny's evolution chain is a two tier chain with Lopunny being the final form. In order to get a Lopunny you must first raise up your friendship with a Buneary. Because its base friendship is lower than most Pokémon, strangely matching that of most Legendary Pokémon, it'll take a little bit of extra time to get there, but the wait is definitely worth it. In Pokémon Omega Ruby/Alpha Sapphire Lopunny can evolve once more using Mega Evolution.
Introduced in Pokémon X/Y Mega Evolution is a new form of evolution that can cause a Pokémon to evolve once more. If the trainer has a Mega Ring (XY) or Mega Bracelet (ΩRαS), a high friendship with the Pokémon, and the appropriate Mega Stone as their held item, a Pokémon can use Mega Evolution. A Pokémon that Mega Evolves can gain access to new Abilities and changes to their types, giving Pokémon battles a whole new twist. Unlike normal evolution, however, it is not permanent and the Pokémon will revert back to its normal form once that battle is over. Mega Evolution is also not without its limits as it can only be used once per battle. So if a Pokémon has already Mega Evolved that battle another one cannot Mega Evolve as well.
Another thing too is Mega Evolution is limited to a small number of Pokémon, so not just any Pokémon can use it. Although Lopunny cannot Mega Evolve in Pokémon X/Y, it can in Pokémon Omega Ruby/Alpha Sapphire. Truthfully, I did not know about this until some time after the game's release. It was only after I played Pokémon Shuffle that I actually learned this. But yeah, to Mega Evolve Lopunny you'll need a Lopunnite which you can get from Mauville City from a dude on the second floor which you can only access after you have become the Champion and have helped Watson with a problem at New Mauville. I'm not exactly sure what's all involved with it––if anything at all––as I had completely missed the guy first time around when I was there and I was sure I checked everything.
Also, I must confess: I fell in love with Lopunny because of Mega Lopunny. I absolutely love the physical look of it. In addition to its kick ass appearance, Mega Lopunny gains a boost to its Attack, Defense, and Speed stats. It also gains the Ability Scrappy which allows its Fighting and Normal-type attacks to hit Ghost-type Pokémon who are normally immune to those types of attacks. No more fear of Ghost Pokémon! Mega Lopunny also gains the Fighting-type in addition to its existing Normal-type.