Marsh (マシュー Mashū?) is the secondary antagonist of Doki Doki! Pretty Cure: Mana Kekkon!!? Mirai ni Tsunagu Kibō no Dress. He is the human form of Mallow (マロ Maro?). Later on, it is revealed that the main antagonist is actually the Clarinet, who manipulated him.
Four years prior to the season, Marsh was originally Mana's dog, Mallow. A classmate from Mana's elementary school found him so Mana adopted him. He always greeted Mana affectionately when she returned home from elementary school. Sadly he tried to run after Mana as she was visiting her hospitalized grandmother but ended up being hit by a car, dying in the process.
After making a contract with Clarinet, Marsh came to Earth in order to trap everyone within their memories for eternity, and was ticked off by how Mana couldn't recognized him. The Cures confront him but his servants of the unremembered overwhelm them. He sends them into their memories in hopes that they will forget about the future.
When the Cures escaped the film theatre, he was irritated and transformed into his true form. Cure Heart noticed the heart-shaped collar, and realizes that Marsh was Mallow the whole time. Mana refused to fight her dog, resulting in her receiving a bite on her shoulder. Mana then apologized because she had realized his feelings, which turns Mallow back to normal. Afterwards, his Clarinet wishes for Marsh to kill the Cures but he refused, saying his name is Mallow. The Clarinet takes them into the future, in hopes to stop it from occurring.
Once Heart and Mallow were deep within the fortress, the Clarinet began shooting gears at them. When a gear almost hit Heart, Mallow sacrificed himself to save her and tells her that she must not feel sad before his body vanishes and only his psyche remains. His psyche was later sent back to heaven, along with Bebel. Mana wonders if she will ever see him again.
He has white hair and red eyes and appears to wear a mask. He also wears a purple robe and plays the clarinet to affect everyone's memories.
In his debut, he is cunning to alter the people's memories and have his servants, Mannequin Carmine, Silver Clock and Purple Buggy to attack them. But as the story unfolds, it is revealed that he still cares deeply for Mana.
His clarinet can make all abandoned objects form into whale-like airships.
His attack is "Eleven Fang" which summons eleven small dog spirits to attack. He can transform into a dog that resembles Mallow.
- Marsh's name when he was a villain comes from the first name Mana gave him, which was "Marshmallow" because of his white fur. She later changed this name to "Mallow".
- He is the third pet to be owned by a Cure in the franchise, preceded by Chuutaro and Korone.
- He is, however, the first pet to die before the series began and only appeared in the movie.