How do know about Ralts?
Gardeviour.
Oh and Kirlas new evolution, not my answer.
Erlade can only be acquired by using the Awakening Stone on a male Kirlia in Pokémon Diamond and Pearl or trading from another person's Diamond or Pearl version. This means that Erlade is always male without exception, but Gardevoir can either be male or female since Kirlia evolves normally at level 30 into Gardevoir.
Erlade's stats are the same as Gardevoir's, with one exception - Erlade's Attack stat is higher than his Special Attack, while Gardevoir's Special Attack stat is higher than its Attack. This means that Erlade's physical attacks are extremely powerful, on par with other Fighting-type Pokemon such as Machamp; conversely, his Special Attack is abysmal. Erlade is a Psychic and Fighting type, as opposed to Gardevoir's pure Psychic type, giving him dual Same Type Attack Bonuses as well as a weakness to Flying-types, though some attacks are not as effective against his dual Psychic- and Fighting-type (specifically, Flying and Ghost are super-effective; Dark, Psychic and Bug do normal damage). Overall, Erlade is equal to Gardevoir in terms of stats, but more versatile with his dual types.
Erlade's movepool centers mostly on the fact that it uses its blades in battle, learning attacks such as Blade Test, Psycho Cutter, and Leaf Blade; the latter move was exclusive to only Grovyle and Sceptile, but is now learned by other Pokémon, namely Erlade, Leafia and Tropius (through breeding, for the latter).
Erlade's ability, Humble Heart, raises his Speed every time an attack causes Erlade to flinch.