After Kanto, Johto, and Hoenn, Ash went onto the fourth region, known as Sinnoh, and dove into the fourth generation of Pokémon. Like his departure from Johto to Hoenn, Ash left all of his Pokémon caught in the Hoenn Region at Oak's lab at the end of the Battle Frontier saga, with the exception of Aipom. Ash began another fresh start with the Sinnoh Region.
He caught several Pokémon in the Sinnoh Region, certainly more than the five he caught in Hoenn. Many were powerful heavy-hitters while others never really measured up. Today, we are going to count down all of the Pokémon Ash caught in the Sinnoh Region from least powerful to most.
6 Gible
Gible was a wild Pokémon that took to following Ash around. Ash eventually caught it, and the Pokémon was immediately used to battle Barry's Empoleon. Unfortunately for Gible, it proved no match for Empoleon.
It swiftly mastered the move Draco Meteor and managed to take down a Shuckle at the Lily of the Valley Conference, and it even went on to defeat a powerful Dusknoir in the same battle. It took on the Legendary Pokémon Darkrai during the Conference as well, but it was unable to beat it.
5 Gliscor
Ash caught Gliscor when it was still a Gligar and trapped, alongside several other Gligar, by the tall buildings of a city. One of Gligar's first battles under Ash was against a Gliscor, which frightened Gligar as it is the Pokémon's evolved form. Gligar later used a Razor Claw item to evolve into Gliscor to save Ash from Team Rocket.
It won Ash a victory over Gym Leader Byron's Bastiodon, but it followed that up with a streak of devastating defeats. Eventually, Ash left Gliscor for further training with fellow Pokémon Trainer McCann. Ash retrieved Gliscor in time for the Lily of the Valley Conference, where it took down McCann's own Drapion.
4 Buizel
Buizel was initially caught and used by Dawn, but she traded it to Ash for Aipom when they realized Aipom's affinity for contests and Buizel's for battling. Buizel immediately proved its worth by tieing in a double knockout against Gym Leader Maylene's Lucario. Buizel also got Ash far in the Pokémon Contest at the Wallace Cup and took out a Kecleon at the Battle Stage.
Later, Buizel went on to fight against Water-type Gym Leader Crasher Wake. He was able to take down the Gym Leader's Quagsire with a powerful combination of the moves Ice Beam and Aqua Jet. Wake then sent out Floatzel, the evolved form of Buizel. With the tag team help of Pikachu, Buizel was able to win this battle as well. From there, it took down Gym Leader Fantina's Gengar, though it lost to her next Pokémon, Drifblim.
3 Torterra
Ash caught Torterra as a Turtwig early on in his journey through Sinnoh. It very quickly showed its worth against Gym Leader Roark's Cranidos/Rampardos and took out Gardenia's own Turtwig in their official Gym battle. It later saved Paul's Chimchar from a Zangoose shortly before Paul released the Chimchar and Ash became its new trainer.
Turtwig evolved into Grotle while battling against Paul's Honchkrow. It later dominated against a Rhyperior when Grotle learned it could power itself up by swallowing its own Energy Ball attack. Grotle finally evolved into Torterra when Ash's battle against Gym Leader Volkner was interrupted by Team Rocket. Unfortunately, Torterra's victories would become few and far between from here on out.
2 Staraptor
Ash caught Staraptor as a Starly, and it was the first Pokémon that Ash caught in the Sinnoh Region. Ash found the Starly after it was weakened in a fight with a wild Aipom, and he took the opportunity to catch Starly, as Pikachu was currently being held by Team Rocket. Starly evolved into Staravia not long after in another showdown with Team Rocket. Staravia was beaten in an unofficial battle against Gym Leader Gardenia, but he scored a win for Ash in the official rematch against a Cherubi.
He was beaten by Gardenia's Turtwig though. Later, Staraptor took on Gym Leader Maylene's Machoke and Meditite, mastering the powerful Flying-type move Brave Bird in the process. During the PokéRinger contest, Staravia evolved into Staraptor on Ash's behalf, beating a Honchkrow in the process. Staraptor later took down Gym Leader Candice's Medicham and beat Paul's Torterra during a championship match. He also took out Pokémon Trainer Nando's Roserade with a single Brave Bird hit.
1 Infernape
Infernape made his first appearance as a Chimchar under the care of the brutal Pokémon Trainer Paul. He often put Chimchar in impossible scenarios and put it through a cruel training process. After several losses, Paul released Chimchar, but Ash invited Chimchar to join him. The Pokémon accepted. Ash and Paul were later paired up in a battle competition. Ash chose Chimchar to team up with Paul's Elekid, and the two managed to take down a Heracross and a Buizel.
Chimchar later protected Pikachu by taking a Poison Jab from a Toxicroak belonging to Saturn of Team Galactic. During a battle with Barry, Chimchar took down a Staraptor. During Gym Leader challenges, Chimchar took out a Mismagius, a Bronzor, and an Abomasnow. In another battle against Paul, Chimchar took out Ursaring and evolved into Monferno, but he then lost to Paul's Electabuzz. Monferno evolved into Infernape to save Ash's other Pokémon from Team Rocket, and it went on to beat Gym Leader Volkner's Jolteon and Luxray. During the Lilly of the Valley Contest, Infernape got more retribution against his former trainer by taking out Paul's Aggron, Ninjask, and Electivire.