There are a few episodes where Pikachu acts out of character or displays unusual behavior, but it's usually due to:
* Misunderstandings: Like in the episode "The Battling Eevee" where Pikachu is accidentally swapped with a mischievous Eevee, leading to confusion and some trouble.
* External Influences: Like in "The Power of One," where Pikachu is temporarily possessed by the spirit of a legendary Pokémon, causing him to act strangely.
* Exaggeration: Some episodes might play up Pikachu's mischievous side, exaggerating his typical playful antics.
It's important to remember that Pikachu is a beloved character and the writers wouldn't permanently change his core personality. He remains a loyal and brave companion to Ash throughout the series.