Kellyn's strongest Pokémon, Raichu has been seen quite frequently with Kellyn. He was first seen in a battle with Canalave City gym leader Byron against his powerful Pokémon. He managed to effectively knock every single one of them, winning the badge for Kellyn. He was then used in the Sinnoh League, and seemingly helped Kellyn make it to the Top 8. After he narrowly defeated Ben's Rhyperior, he again helped Kellyn advance to the Top 4 where he was defeated by Avery's Moltres.
Kellyn's first Pokémon used in the Sinnoh League battle against Ben, Corsola is a strong battler that managed to easily defeat Ben's Staryu in a Spike Cannon and Tackle combination move. It was eventually defeated by Ben's Magmar's Fire Punch.
Mismagius was used in the Top 8 battle against Ben. Mismagius was proven to be a strong Pokémon as she knocked out Ben's Ninjask with just her Shock Wave. She, however, was brutally defeated by Ben's Magmar despite the two Pokémon battling for a long time.
Sunflora was used in Kellyn's battle against Ben in the Top 8 of the Sinnoh Pokémon League. She is a strong battler as she managed to defeat Ben's Sableye quickly with only using Leaf Blade and Razor Leaf. She was then defeated against Ben's ace, Torterra in a draw after their Solar Beam and Hyper Beam fused together.
Muk was used in the Top 4 battle against Avery. It is a relatively strong poison type Pokémon as it knows moves such as Focus Punch and Gunk Shot. Despite being the second to last Pokemon left in Kellyn's team, Muk was defeated by Avery's Moltres.
When Kellyn was about to bring out his fifth Pokémon, Izzy's Venonat accidently fell from the stadium seats, becoming an enlisted Pokémon on Kellyn's team. At first confused, Kellyn didn't know what to do with it. Eventually, Venonat tried using Stun Spore to paralyze Ben's Magmar but failed. When trying to use Psychic, Magmar used Flamethrower on Venonat, quickly knocking it out.
Kellyn used Rhyperior for his Top 4 match against Avery. Rhyperior listened more to Kellyn, helping him take out two members of Avery's team back after back. Eventually, it came down to Rhyperior and Avery's Moltres, where Moltres beat out Rhyperior after a long fought battle.