Serena officially joins the group in their travels.
Poliwag's appearance in Serena's flashback as a Pokémon that Ash found in his youth parallels the Pokémon Adventures manga, as Red found a Poliwag as a child, which he caught as his first Pokémon.
Serena encounters Team Rocket for the first time.
Serena tells Ash about the first time they met, and Ash finally remembers her.
In the Japanese version, this is the first episode of the XY series where the title card is focused on someone other than Ash. The title card for this episode focuses on Serena. This is not the case in the dub as the title card segment still focuses on Ash and will do so regularly starting with this episode.