"During the episode of Pokémon Smash today, some further details of the upcoming series Pokémon XY were revealed. Within this, it confirmed that Ash will be joined on his journey by Clemont and Bonnie, with Serena and Viola being showcased with them. It also confirmed that Jessie, James and Meowth will be following Ash to the Kalos region. It also showed Ash seeing Mega Blaziken and a Garchomp going through town in a rage"
According to Serebii Clemont will be travelling with Ash, however it is not 100% sure that Serena will be travelling with Ash, though she was seen alongside with him