Ash has accomplished some pretty crazy things over the course of the Pokémon anime, but it turns out that he might've had help with some of those feats, thanks to a special power he was revealed to possess: Aura.
Aura is a technique most prominently used by Lucario and Riolu, two Fighting-type Pokémon introduced in generation 4. The Pokédex states that Lucario and Riolu can see these auras, which represent the life energy of both people and Pokémon, and manipulate them. In that way, Aura is quite a lot like the real life concept of Chi or Ki, which similarly has martial arts applications. While other Pokémon, particularly Fighting types like Lucario, are able to use Aura, the ability is still closely associated with its first users, so much so that Lucario's mechanics in Super Smash Bros. are based around Aura.
In the two-part episode "Pokémon Ranger and the Kidnapped Riolu!", Ash first demonstrates this ability by being able to see the Aura around Riolu when he meets it. It's said that the ability for a human to see an Aura is quite rare, but the ability to manipulate it is even rarer. Only one other character, Riley, is shown to be able to manipulate Aura. A human user of Aura is said to be capable of detecting thoughts, both seeing and "sensing" the Aura of other beings, connecting telepathically with others (including Pokémon), share their own energy, and even form energy barriers or attacks. It's later revealed that it also has a connection to Mega Stones, making it possible to sense them from a great distance away. At the episode's end, Ash is offered the chance to train and develop his Aura power, but he declines in favor of continuing his journey.
Ash's Aura Explains His Coolest Pokémon Moments
That isn't the last fans hear of Aura, however. Ash's Aura became prominent again in Journeys, where Ash obtained an egg that would go on to hatch into Riolu. Ash and Riolu worked together to train its Aura power, which also enhanced Ash's own. After it evolved into Lucario, Ash and Lucario worked with a Kalos Gym Leader, Korrina, to locate a Mega Stone for Lucario using Aura. Lucario is even shown communicating telepathically with Ash mid-battle, giving recommendations on what moves to use. The Aura ability also seems to have been used by Ash's Greninja, and the special Bond Phenomenon may have occurred specifically because of Ash's Aura, connecting their life forces. While it's not known how Ash's Aura affected his other Pokémon, if at all, it certainly would explain some things, like how his Pikachu is so incredibly powerful. There's even a suggestion that Ash may be descended from or a reincarnation of a famous Aura user named Sir Aaron, meaning that even among Aura users, he's particularly powerful.
While not every achievement of Ash's can be chalked up to his special powers, they've clearly played an important role in his success by allowing him to bond with his Pokémon in unique ways and empower them in ways that others can't.