Muffet is the Royal Scientist.
Muffet is a nerdy, shy recluse with a fondness for anime. She has a crush on multiple characters, but often has trouble exploiting her feelings. She was told by Queen Undyne to inject Determination into monsters who had "fallen down", unfortunately, the Determination and Monster souls were not compatible and melted the monsters she had experimented on, turning them into Amalgamates. She locked them under her lab and has told nobody, and has fallen into depression.
Unlike the two pigtails of Her classic version, she wears her hair in one bun. She has 6 arms and 5 eyes. Her hair is black, her skin is lavender and her eyes are purple.
When first meeting her, she's wearing a pink one piece bathing suit-type type of clothing, and over that, a white lab coat. She wears magenta shoes. On her date in the True Pacifist, she's wearing a magenta dress with white polka dots. In the Epilogue, she's wearing her pink bathing suit and no shoes.