A member of Varia, Viper is also an Arcobaleno who is very skilled when it comes to illusions.
Viper with his partner Fantasma
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 theMammon 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.
Viper vs Chrome
During the Ring Conflict, he defeats Chrome Dokuro with no problems; however, he is defeated by Mukuro Rokudo 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.
Arcobaleno Trials Arc
Viper is the third administrator of the Arcobaleno Trials. He and Belphegor enroll in Tsuna's school for a time, using the psuedonyms Monta and Himeko Hariyama. Later, Yamamoto discovers this when Himeko throws some of Bel's signature Knives to protect himself and Kyoko. Viper's Trial involves battling Tsuna, Ryohei, and Yamamoto. In the Trial, he uses his special Ability: Viper Mirage. Everyone was surprised when they heard Verde told Viper to test out a prototype Box Weapon. Reborn said that he had a bad feeling about this. During Verde's trial, Viper attempts to stop a Pawn missile from making it to Namimori, although his efforts were thwarted by a substance which was later revealed to be similar to the Non Tri-Ni-Sette, which Verde uses to capture the rest of the Arcobaleno, sans Aria. Unlike the actual Non Tri-Ni-Sette, the substance only paralyzes them, as opposed to outright killing them. It later turns out that the captured Arcobaleno were revealed to have been Illusions done by Viper as soon as he saw the substance released again when all the Arcobaleno were present.
Inheritance Succession Arc
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.
Inheritance Ceremony Arc
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.
~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.
~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. (exept the sky ring)
~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.