Kalos was the sixth Pokémon region and accompanied the sixth generation of Pokémon. Ash journeyed here during the Pokémon X & Y series and teamed up with fellow travelers Bonnie, Clemont, and Serena. This is also the generation that introduced Mega Evolution to the Pokémon canon.
Like the prior regions, Ash made a fresh start in Kalos, keeping only his Pikachu on the journey. He caught a team of new Pokémon while in Kalos, with some rising to the top while others did little to help Ash advance in the Kalos Gym challenge. We are going to rank Ash's Kalos catches here today, from worst to best.
5 Noivern
Noivern was found as an egg by Ash's Hawlucha, and it hatched into a Noibat. It and Hawlucha were kidnapped by Team Rocket not long afterward, and the two had to work together to escape. Noibat learned how to fly better from Hawlucha and through participation in a Flying-Type Pokémon race. It finally evolved in a battle with the Legendary Pokémon Zapdos.
It held its own against the rampaging Zapdos until Team Rocket captured Zapdos, and Noivern and Pikachu freed Zapdos and defeated Team Rocket again. Noivern later battled Pokémon Trainer Sawyer's Doublade but lost to his Clawitzer. Later, when Lysandre's plan came to fruition, Noivern fought against his Pyroar and Mega-Evolved Gyarados. When Gyarados launched a Dragon Tail attack, Noivern took the attack on Pikachu's behalf, allowing Pikachu to keep fighting the battle.
4 Hawlucha
Hawlucha started off as the Champion of the Forest, a guardian to a community of Pokémon. However, a nefarious Ursaring and Conkeldurr began stealing food and blaming it on Hawlucha. Ash encountered Hawlucha and helped clear its name with the other Pokémon of the forest, and Hawlucha joined up with Ash after a Machamp took up the Champion of the Forest mantle. Hawlucha quickly helped Ash against Team Rocket and later took down Gym Leader Korrina's Mienfoo before being knocked out by her Mega-Evolved Lucario.
Hawlucha took part in a staged wrestling match-esque battle called Carl's Super Pokémon Battle that ended with a very real battle against a shiny Hawlucha. It came in handy in Gym Battles, taking out Ramos' Weepinbell, Clement's Heliolisk, and Valerie's Spritzee. After Ash caught Noibat, Hawlucha served as a mentor for Noibat, teaching it how to fly, gain speed, and battle better. Hawlucha later proved invaluable by taking out a Mega-Absol and later a Weavile in the Lumiose Conference. Hawlucha also participated in the climactic battle against Lysandre's Mega-Evolved Gyarados.
3 Talonflame
Ash encountered Talonflame as a Fletchling, and Froakie fought Fletchling so Ash could catch the Flying-Type Pokémon after it stole a berry from Bonnie. It later struggled in the challenge against Gym Leaders Viola and Grant. Eventually, Fletchling entered a sky battle against a Talonflame, which is the final form of Fletchling. Fletchling evolved into Fletchinder and actually defeated the Talonflame. As Fletchinder, it scored a trio of victories in Gym battles against Korrina's Machoke, Ramos' Jumpluff, and Valerie's Sylveon.
It battled against the Legendary Pokémon Moltres, though it was badly outclassed. Fletchinder evolved into Talonflame during the fight, but it still didn't achieve victory. It teamed up with Frogadier to fight Olympia's duo of Meowstics and won the battle, and it battled another Legendary Pokémon in Zapdos. It scored another Gym challenge victory in Ash's rematch with Wulfric, when it defeated the Ice-Type Avalugg. In the Lumiose Conference, Talonflame took out a Slaking before being defeated by Clawitzer.
2 Goodra
The Dragon-Type Pokémon Goodra first came into Ash's life as a Goomy that was driven from its home by a swarm of Bug-Type Pokémon led by a Florges. When it found Ash and his friends, Goomy was weak from the experience. After being healed and helping Ash and his friends against Team Rocket, Goomy joined up with Ash.
Goomy started off afraid of Ash's other Pokémon, but it grew to trust them after another showdown with Team Rocket. Eventually, Goomy evolved into Sliggoo while helping Ash take on Team Rocket and a rampaging Grumpig. During another attack from Team Rocket, Sliggoo evolved into Goodra while saving his friends from a fire. Goodra went on to team up with Pikachu and defeated a Raichu and Wartortle belonging to Tierno, Ash's rival in the Kalos Region.
Goodra was one of Ash's choices for the Lumiose Gym battle, and it took on Gym Leader Clemont's Luxray in the battle's climax. A mixture of Rain Dance and Bide helped Goodra win the battle and earn Ash the Gym Badge. Eventually, Ash's journey brought Goodra back to the wetlands it once called home, and Florges and its army of Bug-Type Pokémon allied with Team Rocket. Goodra battled against Florges and the Bug Pokémon, but Team Rocket ended up betraying Florges. This lead to Goodra and Florges teaming up to defeat Team Rocket and making peace. After this, Goodra decided to stay in the wetlands to protect its home. However, it did return to help Ash during the Lumiose Conference and aided against Lysandre and Team Flare - teaming up with Pikachu at a pivotal moment to take out Lysandre's Gyarados and Pyroar.
1 Greninja
Greninja met Ash as a Froakie and was the first Pokémon to join Ash in the Kalos Region. Froakie helped Ash capture Fletchling and Hawlucha, and Froakie took out Gym Leader Grant's Onix. Froakie eventually evolved into Frogadier while saving Sanpei and his Greninja from Barbaracle, which is the partner of Sanpei's mentor Saizo. Frogadier won Ash more Gym battles against Ramos' Gogoat, and teamed up with Talonflame to take out Olympia's two Meowstic's.
Eventually, Frogadier evolved into Greninja during another encounter with Sanpai while battling a Bisharp. Greninja's bond with Ash became so strong that it developed a pseudo-Mega Evolution called Ash-Greninja while battling Pokémon Trainer Sawyer's Sceptile. With the help of Clemont and his Luxray with Alain and his Charizard, Ash and Greninja tested out this synchronicity, which would drained Ash as well as Greninja.
Ash and Greninja went on to beat Gym Leader Wulfric's Abomasnow, and they championed over an Altaria, Sawyer's Sceptile, and Alain's Bisharp. When Lysandre and Team Flare began their takeover plan, Ash-Greninja and Pikachu were pivotal in taking down Lysandre's Mega-Evolved Gyarados and helped take down the Giant Rock.