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Viper is the holder of the Indigo Pacifier. He is a member of the elite Vongola assassination team, the Varia, under the name Mammon (マーモン). Known as the Arcobaleno's best spellcaster, Viper has the ability to cast illusions, as well as being able to locate any person by sneezing into a piece of paper (he carries a roll of paper with him); the spit or mucus that sticks to the paper shows a map leading to the desired person. Other than for the exception of the Arcobaleno trials, Viper only works for money and is therefore represented as the sin of greed in Varia. He also has a black frog named Fantasma that lies on top of his head. By turning into a yellow ouroboros (a snake devouring it's own tail that is also an alchemist's symbol) into a "halo" above him, Fantasma can give Mammon the ability to fly in combat. He claims to have been trying to break the Arcobaleno curse, and had sealed his pacifier so that other Arcobaleno cannot sense him with the Mammon Chain, which also seals the power of Rings and Boxes and such. The Chain is replaced by the Vongola by the cap that conceals the Rings' powers the same way as the Chains.
During the Ring Conflict, he defeats Chrome Dokuro with no problems; however, he is defeated by Mukuro once the latter takes possession of Chrome's body. Although, he managed to survive because he reserved enough energy for him to escape at the beginning as a precaution.
Viper and the other Arcobaleno are called by Reborn to train Tsuna and the others. Viper is paired up with Chrome as his student. But, it seems that Viper hasn't taught anything to Chrome due to the fact that he doesn't get paid. So, right after he comes back, after hearing his insults from Skull, he leaves. However, he comes back when Colonnello was searching for him and later helps Chrome to break Daemon Spade's Illusion. After Daemon and Giotto gave Chrome and Tsuna their inheritance, Chrome thanked him for saving her, and he said that she had improved, somehow. Shortly, he was picked up by Squalo and Belphegor who had searched for him everywhere because there was a job that required an illusionist.
At the ceremony, he noticed that Dino and Squalo had seen through Chrome's illusion of Yamamoto; however, he tells her that an illusion of that level can be only seen through by experts and assures her that she was doing well. At the last minute right after Tsuna and the others were defeated by the Shimon, he and the rest of the Varia along with Dino and Reborn, tried to stop the Shimon but was stopped by their tracks by Adelheid. Squalo requested for him and the rest of the Varia to chase after the Shimon right after they took Chrome away, but the Ninth order them not to chase after them.
Before he was turned into an Arcobaleno, he was a first-class psychic who added Illusions to his repertoire. It was seen he could also fly before he was turned into an Arcobaleno. His psychic Abilities were telepathy and he could also dowse things through photographs, so that he could find things and people. As an Arcobaleno he still has all his Powers, but his Illusions have been strengthened, possibly because the Arcobaleno´s Mist Pacifer is a Ring that emits Mist Flames, creating real Illusions, and the Arcobaleno's ability to emit Dying Will Flames from their bodies. In one occasion, he even showed that he could teleport.
- Illusions: As the Mist Arcobaleno his Illusions are first class, the only time he was defeated by another Illusionist was when he fought Mukuro. His favorite Illusions are Illusions of clones of himself and the Illusion of tentacles.
- Viper Mirage: One of Viper's many Illusion abilities, he used this to surround Namimori with a series of mirages.
- Telepathy: One of his psychic abilities is telepathy, the ability to read minds.
- Thoughtography: The ability to locate any person by sneezing into a piece of paper; the spit or mucus that sticks to the paper shows a map leading to the desired person.
- Flight: Thanks to his pet Fantasma he can fly, but he has been shown to be able to fly before he got Fantasma.
- Mammon is a term used to describe material wealth or greed, most often personified as a deity.
- In the Reborn! Fandom, his letter is V.
- He dislikes being called by his given name, Viper. But, he doesn't seem to be mind if Reborn calls him by his given name.
- Mammon loves money and thus represents Greed from the Seven Deadly Sins.
- Mammon only works if he gets paid. However, he will work if the situation is dire or to do his duties as an Arcobaleno.
- Mammon's gender has been a debate among fans, due to the use of gender-neutral pronouns used to describe him. He was grouped into the male character category in the third popularity poll, and his gender continues to remain as male in the official VIZ translations.
- Mammon has a character song, Maboroshi no Arcobaleno.
- During the Sky Match when Xanxus has been frozen by the Zero Point Breakthrough, he seemed to have the Ability to light all of the Vongola Rings.
- He seems to be in good terms with Belphegor since they were almost always seen together. However, in the Vongola 77 databook, Belphegor describes Mammon as " An irritating Chibi, " implying that the two have a teasing relationship.
- In the Inheritance Succession Arc, he doesn't seem to have any qualms about training Chrome despite the fact that he had nearly been killed by Mukuro before, and even helped Chrome by encouraging her on her Yamamoto illusion.
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