The split personality (忍法疑心暗鬼にご用心の巻) is episode 561 of the 1981 anime.
When Hattori hypnotises Kenichi, he undergoes a horrible personality change - leaving Hattori to clean up the mess.
Synopsis []
Kemumaki decides to prank Kenichi by telling him that Yumeko called him to the library. Kenichi gets so flustered that he falls off the monkey bars in his rush to get to the library. When he gets to her, he speaks to her in a loud and genial tone, and Yumeko tells him to tone it down as everyone else is reading. Kenichi is furious with Kemumaki when he realises that it was a trick.
Back at home, Kenichi tells Hattori what he's been through; Hattori tells him that he can put a spell on him to change his personality. Taking an old red mirror out of a purple box and drawing a grim, sullen face on it, he turns it around several times in front of Kenichi's face until his face turns glum and sulky too. He tells Hattori that he feels just the way he wanted to.
A few hours later, Kenichi accompanies his mum to the supermarket where he openly expresses his doubts about buying meat and grapes. Amid the laughing of amussed customers passing by, Mrs Mitsuba blushes, then faints. On their return home, they bump into Mr Mitsuba, who announces he'll be going abroad on a work trip for a few days so he'll need some documents. Kenichi fears that he will get sacked if he doesn't find them. Everyone is horrified.
Kenichi goes up to his room to clear his head. There he snatches back his comics from Shinzo and Shishimaru. They make a monkey out of him, so he kicks them out and locks himself in.
Downstairs, Shinzo, Shishimaru and Mr and Mrs Mitsuba turn on Hattori and furiously order him to get Kenichi back to normal. Hattori immediately goes upstairs and tries to persuade Kenichi to come out of his room. When Kenichi refuses, Hattori barges in and de-hypnotises him. Kenichi becomes his cheerful self again and goes downstairs to join the others. As Hattori follows him, Kagechiyo sneaks in and nicks the mirror. Taking it to the flat, he hypnotises Kemumaki - and he becomes insufferably chirpy.
The next day, an unsuspecting Kenichi tells Kemumaki that Yumeko wants to talk to him. Kemumaki gets overexcited and dashes off to meet her; Kenichi is shocked.