Muffy's dog

Giselle is a white poodle owned by Muffy. The dog appears in "Poor Muffy" and "Crushed".

D.W., the Picky Eater
The dog is mentioned in "D.W., the Picky Eater," when Arthur and his friends are trying to come up with ideas on how to get D.W. to like spinach. Muffy suggests:

"D.W. just has to see somebody she admires eating spinach. Trust me, that's how our butler got our dog to try a new brand of dog food."

It also appears in "Crushed" in the beginning. According to Buster's song, the poodle is a 'he'.

Amigo revealed his name in an unknown episode of Arthur. She was mentioned.