Hajime's Mother

Arnold's mother is a character of the day who appeared in Hypno's Naptime.

Arnold's mother mistook Ash for her son, Arnold. She revealed that Arnold, like the other children, had disappeared three days before Ash and his friends had arrived to HopHopHop Town. Unbeknownst to her, this was due to a Hypno's sleep waves, which were being used by socialites to treat Insomnia and as a novelty. The sleep waves had unintentionally affected a larger area than desired, and had brainwashed several children into believing they were various Pokémon. They all had gathered in the park, imitating the Pokémon they believed themselves to be, until Ash and his friends, upon discovering their location and the cause of their strange behavior, brought Drowzee to the children. Drowzee promptly undid the brainwashed behavior, and the children returned to normal and reunited with their parents, including Arnold.

(Source: Bulbapedia)