During the opening ceremonies of the Indigo League, Moltres itself shows up and lights the torch.
Who are we kidding; the whole premise is one!
Ash's Squirtle is a walking, talking, Tengen Toppa Gurren Lagann reference. Worse? He's memetic. Gary is initially angry that Ash's Squirtle turned his Squirtle into post-time-skip Simon (not literally).
Just seeing Ash going mano-a-mano against Pokemon on his own is one.
Even if he lost, Ash did put up a pretty good fight against Lorelei, who in canon beat him up, down and sideways without much effort. This time, Ash managed to bring Lorelei down to her last Pokemon and only lost because Jynx's Focus Sash allowed her to barely endure Tauros' Fissure.
A slight one for the author by managing to get a pretty accurate guess on how Keldeo would be depicted well before his featured movie was released.
Ash giving Mewtwo a run for his money in one-on-one combat.
The way he does it is awesome too. Ash needs to use Ghost type moves to do any damage to Mewtwo, a Psychic type, and he figures out how to do that. How? His own blood. And by the end, he was almost out of it, and nearly died from blood loss. Ash was fully prepared to put his life on the damn line and possibly die to knock some sense into Mewtwo.
He actually did die, but the Sacred Ash brought him back. Doesn't diminish the awesome, though.