Matthew came to Earth and rewrite the Cures' memories (except Aguri) to forget each other and remember their childhood. The Cures overcome their past to defeat him. He and Maro transform into a dog to fight them. Cure Heart was injured and the Miracle Lights encourage her and she changed into her Engage Mode to defeat him.
He has white hair and green eyes and appears to wear a mask. He also wears a purple robe and plays the clarinet to affect everyone's memories.
His flute can alter peoples memories. When he and Maro merge together, he becomes an enormous dog. His attack is 'Eleven fang' which summons eleven small dog spirits to attack. He can transform into a dog that resembles Maro.
Marsh's name when he was a villain comes from the first name Mana gave him, which was 'Marshmallow' (She later changed this name to Maro.)