Pokémon anime's Ash has trained several Pokémon to be the strongest ever. Ash has also encountered powerful Pokémon, some of which he unlocked.
A unique bond between Ash and Greninja let the two to morph into something akin to Mega Evolution when they engaged in combat.
1. Greninja's Bond
Ash's most famous Pokémon after Pikachu, Charizard, was found as a dying Charmander in the rain. After evolving, it respected Ash's work but didn't obey him.
2. Charizard's Power
Ash became a Chimchar and got Infernape after Paul left, a big achievement. After being called "too weak," Ash trained Chimchar to fight fiercely in every situation.
3. Infernape
Ash's new Pokémon Journeys egg-reared Lucario. Due to Ash's ability to perceive Pokémon auras, Lucario and Ash clicked right away and trained well together.
4. Lucario'
Ash met his Sceptile as a Treecko and helped defend its habitat. Since its Overgrow ability made it powerful when the chips were down, Ash often used it last to win.
5. Sceptile
Ash helped Goodra, a Goomy that fell into Ash's lap, grow stronger and bolder. Hydration helped Goodra recover from status disorders in the rain several times.
6. Goodra Bravely
Since Hawlucha was a forest protector before joining Ash, Ash favored him in Kalos. Ash defeated Hawlucha's Flying Press more often than not.
7. Hawlucha'
After the scientists finished studying it, Ash was given this weird and powerful Pokémon from a fossil revival gone wrong.
8. Dracovish
Ash has caught Melmetal, a Mythical Pokémon, one of the rarest, biggest, and strongest. When hundreds of Meltans helped Ash win the Alola League, it evolved.
9. Melmetal
In Pokémon's Orange Islands, Ash finds his Snorlax floating between islands, robust from eating everything. Snorlax defeated a big Rhydon with one punch.
10. Snorlax
Naganadel, one of Ash's rarest Pokémon, appeared as a Poipole through an Ultra Wormhole.
11. Naganadel
Ash's Gengar originally appeared in Pokémon Journeys haunting the Cerise laboratory. Ash caught it and performed a ritual to give Gengar Gigantamax.