These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Seriously, you could remove Pichu and replace it with another small pokemon and everything would still turn out the same. To make matters worse, the creators put it on the cover of the film even though it had very little screen time than that of other more notable pokemon.
Descended Creator/What Could Have Been: According to ADR director Tom Wayland, Arceus was originally going to be voiced by actor Vincent D'Onofrio of Full Metal Jacket and Men In Black fame. However, before his recording session, there were difficulties with D'Onofrio's agent and he was unable to record for the movie. After re-auditioning, Tom Wayland himself was chosen to voice Arceus instead.
Hilarious in Hindsight: When Sheena tells the heroes about a legend involving a young trainer with an electric Pokémon, Dawn automatically assumes it's referring to Ash. He isn't so quick to agree however, probably because of what happened the last time he Jumped at the Call.
Some people said that Marcus was the human version of Shadow the Hedgehog when the movie was still in Japan. And now he's voiced by Jason Griffith!
Just Here for Godzilla: There's a part of the audience that skips most of the story just to see the Creation Trio battle against Arceus.
Narm: Thunder creature? Really? Sheena couldn't just say "Electric-type Pokémon" or even Pikachu?!
For some, Arceus' English voice is built out of Narm. Dan Green should have voiced him, not Damos.
What an Idiot: Ash, Dawn, and Brock doing nothing but standing there as Kevin explicitly orders them to escape as Giratina is in the distance fighting Dialga. Then Ash impulsively runs into the lake to get to Giratina. Granted, Giratina doesn't hurt him, but it was still a pretty dumb move when up against the enraged, 14ft tall Eldritch Abomination.