In Crystal-Clear Sleuthing!, Rotom Pokédex was shown to be a big fan of a detective show that Raki starred in and used his knowledge in an attempt to track down Ash's missing Electrium-Z. However, at the end of the episode, it has been revealed that the Z-Crystal had been stuck inside Rotom's wig the whole time.
In SM023, Rotom Pokédex updated itself with a voice duplication function. In SM024, it used this function to give Ash's speech for him during the Visitation Day, as Ash mouthed random words. The cheating was quickly caught, however, when Rotom started speaking faster, and began spitting out phrases from other people, like Principal Oak. Rotom was still happy to have given the speech.
After Rotom inhabited the Pokédex, it seems to have lost all combat functions, and is unable to use any moves. As shown in Crystal-Clear Sleuthing!, it can use the "arms" on the Pokédex to extract data from other electronic devices and now has a video camera function and a voice duplication function.
Compared to previous Pokédexes in the anime, Rotom Pokédex provides Ash with the type of Pokémon it provides data on.