Doraemon (1979)

Season 1: Episode 2

The episode starts with Nobita's mother asking Nobita to buy desserts to treat their visitor. He goes up stairs and finds a box of Transformation Biscuts. He eats a cat shaped one and then takes the box to the visitor, who eats four of the biscuits. Then his mother reminds him to buy the desserts. He then goes to buy desserts and to his shock, turns into a cat for five minutes. Later, Nobita and Doraemon then try to stop his mother from seeing the transformation happening on the visitor. The episode ends with Nobita's father fainting upon seeing that Nobita's mother had turned into a rabbit after eating a biscuit.