Ralts was Gabriel's second pokemon caught in the Hoenn region. He decided to catch it after he had helped Wally catch his Ralts. During his adventures it had evolved into Kirlia then Gardevoir.
Wailord was caught after Gabriel's first battle in Mossdeep City against Tate and Liza as a Wailmer. Due to Gabriel's team relying mostly on Blaziken a Fire and Fighting type, he had a double, disadvantage against their Rock and Psychic pokemon. While fishing after the battle a wild Wailmer was found and soon after evolved into Wailord. Wailord's powerful Water-type attacks were able to easily overpower Tate and Liza's Solrock and Lunatone proclaiming him victorious and the Mind Badge.
Luxray was Gabriel's first catch in Sinnoh. All his friends had caught Starly as their first catch so he decided to be original and catch a Shinx because he hadn't had that much experience with Electric-based attacks
Luxray has been proven to be able to hold its own, and was used to cover Infernape's weakness over Water Pokemon with his Electric attacks, building a strong bond between the two.
Honchkrow was Gabriel's second catch in Sinnoh. All his friends had caught Starly as their flyers so he decided to be original and caught a Murkrow in Eterna Forest.
Honchkrow had been used as Gabriel's main means of transportation and flight.