Call-Back: Ash's room is filled with items he acquired during his Sinnoh journey, including:
The two Soothe Bells he won in the Hearthome Tag Battle competition.
The Focus Band the Stonecutter gave him in Bibarel Gnaws Best.
The wooden Teddiursa doll that May gave him.
His Pokemon Summer Academy diploma.
The certificate he received for winning the Poke-Ringer tournament.
The trophy he won for winning the Twinleaf festival.
Level Drain: Pikachu getting struck by Zekrom's lightning is this. First, Pikachu is temporary unable to use electric moves. Second, Pikachu becomes exhausted faster than usual. Third, he loses to Trip's Snivy at its earliest level; for a Pokemon that has battled legendary Pokemon like Latios and have made it so far in Sinnoh League, this is a major downgrade.
One-Scene Wonder: Zekrom's appearance in this episode marks the only time it appears in the entire anime (aside from a few movies).
Time Skip: Most likely a rather short one, but it's subtly hinted that some time has passed since Ash returned from Sinnoh, given that he's already gotten his new outfit and that his Sinnoh team have already been set up at Professor Oak's Lab. In addition, the Team Rocket trio have been put through new training and promoted to A-Rank agents, resulting in...
After becoming A-Rank agents, Team Rocket gets a more serious demeanor and a serious role.
Despite being a starter Pokemon at its earliest stage, Snivy uses Leaf Tornado, which is learned much later but right before evolving. Also, it defeated Ash's Pikachu.
Worf Had the Flu: The reason that Pikachu lost to a rookie Snivy is that the encounter with Zekrom left him temporarily weakened.
