Continuity mistake: When the dentist wants to put Nemo in a bag, it's a resealable one with a seam at the top. When he finally catches him, it has changed to a normal plastic bag.
Continuity mistake: When Ash and friends are astonished by the view they find at night, Brock is holding his guidebook, but in the next shot, the book disappears. (00:04:04)