Doopliss is a Duplighost that lives in the Creepy Steeple of Twilight Town in Paper Mario: The Thousand-Year Door. He appears as an enemy of Mario several times throughout the game, and is the boss of Chapter 4. He causes the members of Twilight Town to become pigs whenever the bell tolls, and attempts to steal Mario's identity. He has the special ability of stealing another character's body when copying them, something that most Duplighosts are unable to do. He later becomes a member of the Shadow Sirens, replacing Vivian.
 Paper Mario: The Thousand-Year Door
At some point after the Boo of the four legendary heroes hides the Ruby Star in Creepy Steeple, Doopliss moves into the castle and keeps it for himself. Doopliss enchants the bell of the Creepy Steeple so that each time it rings, a resident of the nearby Twilight Town is transformed into a pig. Mario, whose Magical Map tells him that the Ruby Star is inside the Creepy Steeple, seeks to help the inhabitants of the village and goes to the steeple via the Twilight Trail. When Mario and his partners encounter Doopliss in the highest tower of the steeple, he is watching TV and coming up with new ideas for pranks, suggesting that he is a very dedicated prankster.
In the following fight against Doopliss, Goombella is unable to tell Doopliss's name using Tattle, as it doesn't appear in her log. Instead, Doopliss' name is represented by five question marks (i.e. ?????). Doopliss fights by transforming himself into a shadowy outline of Mario and attacking with his moves. After a while of fighting Doopliss, he takes on Mario's actual form and transforms Mario into just a shadow. Doopliss, as Mario, claims to have defeated himself and won the Crystal Star. Having successfully tricked Mario's partners, he marches off to Twilight Town, leaving the actual Mario defeated on the floor.
The real Mario, now merely a shadow, follows Doopliss back to Twilight Town, where he meets the ghost at the village's entrance. Doopliss then tells Mario that if he can correctly guess his name, Mario's original form will be restored. At the moment, he is unable to guess correctly because Doopliss has somehow removed the lower case letter P from the screen. Because of this, he challenges Mario and orders him not to run. However, because neither Mario nor Doopliss can damage each other, Mario is forced to flee.
While in Mario's body, Doopliss decides to claim Mario's efforts for his own. He presents himself to Twilight Town as their savior who defeated the steeple's demon and lifted the pig curse. He visits Mayor Dour, who invites him for a meal. None of the villagers notice Mario's true identity, although his fellow party members note that the fake Mario is behaving in an unusual manner.
Mario then finds Shadow Siren Vivian, who is at the time in Twilight Town looking for the Superbombomb and doesn't realise who she meets is actually Mario. They hear from a crow in the village that a being in the basement of the Creepy Steeple knows Doopliss' name. Back in the steeple, they hear the name "Doopliss" from the parrot living there. The lowercase P, which was not available in the name selection screen provided by Doopliss, is held in a treasure chest in the Creepy Steeple's dungeon. Having secured the missing letter, Mario and Vivian are able to name the ghost correctly.
Mario and Vivian then corner Doopliss at the entrance of Twilight Town and tells him his real name, which weakens the power of his spell by making him vulnerable to Mario's attacks. Doopliss's magic is, however, not fully broken by this and he flees back to the tower of the Creepy Steeple. In the tower room, Doopliss and Mario's fooled partners fight the actual Mario. Vivian only then realizes he is Mario, but chooses to abandon her sisters and joins Mario in the fight. Doopliss is defeated and both he and Mario return to their original forms. Doopliss flees and gives up the Ruby Star. While on the run, he meets Beldam and Marilyn in Twilight Town who were currently looking for Vivian.
Doopliss joins the Shadow Sirens and fills in Vivian's place. In this position he, too, is mistreated by Beldam, who insists on calling him a "freak-in-a-sheet", despite the fact that he is no longer secretive about his name.
Later, he helps the Shadow Sirens at their disruption on the Excess Express. Aptly disguised as the star Zip Toad, he steals the Nitro Honey Syrup from the Businessman. This special syrup supposedly causes an enormous explosion when mixed with calcium and gold, so he prepares its use as a bomb, stealing the Shell Earrings of the Toad Waitress for the calcium part and Toodles's Gold Ring for the gold part, but is stopped in last minute by Mario. When Pennington arrests Zip, and takes him off the train at Riverside Station, he shocks Pennington by turning back and dashing away.
Doopliss, Beldam and Marilyn reappear in Poshley Heights, where they break into the Poshley Sanctum by smashing a window and steal the fake Garnet Star, which turns out to be a red herring created by Pennington.
Doopliss reappears once again after Chapter 7 in the Rogueport Sewers, where he has taken on the disguise of Professor Frankly and tricks Mario and his partners into opening the Thousand-Year Door and going into the Palace of Shadow. The Shadow Sirens and Doopliss fight Mario and company in front of Riddle Tower in the Palace of Shadow. In this battle, Doopliss is a bit tougher, and has the ability to transform into one of Mario's partners and attacking as them. After their defeat, Beldam, Marilyn and Doopliss watch Mario's battle against the Shadow Queen. After this event, he wants everyone to call him by his real name, tired of Beldam calling him a "Freak-in-a-sheet".
At the end of the game, Doopliss changes his mind about being a prankster and becomes an actor, being on stage together with Flurrie. He plays the role of Mario.
 Super Mario-Kun
Doopliss also makes an appearance in the comic Super Mario-Kun. Doopliss plays the same role in Super Mario-Kun as he does in Paper Mario: The Thousand-Year Door. He holds one of the Crystal Stars and steals Mario's identity by using a beam based attack. In the end Doopliss is humorously defeated by the real Mario. After the fight, the real Mario gets his identity back.
 Physical Description and Traits
Doopliss is, in his regular appearance, a Duplighost who wears a blue bow tie and a blue cone-shaped hat with red stars on it. His eyes and mouth appear bigger than those of the Duplighosts in Paper Mario, his sheet is whiter, and his shoes are orange instead of gray. Doopliss is, as a Duplighost, most likely undead. He is referred to as a demon by the inhabitants of Twilight Town.
When he takes on Mario's form, he often has stern and evil looks which are rarely or never seen on the actual Mario's face. When Doopliss impersonates Mario, it is also notable that this is the only time where Mario is actually seen talking, as the real Mario is portrayed as a silent protagonist throughout the game. Even Mario's partners take notice, when both Mario and Doopliss visit Mayor Dour's house. They are surprised and wonder whether Mario suddenly learned to talk. It is also worth noting that at all times that when Doopliss is Mario that he looks rather tired (like Mario when he is in danger or peril), his eyes are more rounded, as opposed to the true Mario's oval-shaped eyes, and that he is slightly shorter than the real Mario. When Doopliss impersonates Mario, Doopliss' voice becomes metallic.
 Powers and Abilities
Doopliss' major ability is to transform into different people. By doing this, he can actually steal the real person's look and name, leaving them just shadows. When Doopliss assumes Mario's form, Mario is unable to tell Vivian his real name, and is only able to confirm it when she confronts him with being Mario. Doopliss states that he can only truly become Mario by defeating the original one. However, this is not always the case, as Doopliss is later able to transform into Mario's partners without them losing their own form. This ability is commonly attributed to all Duplighosts. He can also attack by floating into the air, then swooping down onto Mario and his party.
Doopliss' magic is broken by telling him his name. A crow in Twilight Town states that there always has to be at least one being knowing Doopliss' name; otherwise, he cannot exist. After Mario's victory over him after Chapter 4, Doopliss stops being secretive with his name, however, and apparently, it no longer hurts him when his name is said (at one point, he is even yelling to Beldam "I said, my name's DOOPLISS!"). Conversely, it seems he is afterwards unable to steal one's identity as fully as he did with Mario.
Doopliss somehow enchants the Creepy Steeple's bell to turn an inhabitant of Twilight Town into a pig (similar to a lil' oink) each time it rings. It is unknown how exactly he does it, and it is also never revealed how the curse is lifted. One possibility is that Doopliss' defeat brought the curse down. It might also have been the power of the Ruby Star, and when Mario claims the star, the villagers turn back to normal (the same thing happens with Grubba). However, it is also likely that Doopliss himself turns the villagers back to normal, as he, in Mario's form, claims that it had been him who freed them from the ghost. Also, the bell might still be enchanted, as it is stated that it no longer rings.
When Doopliss corners Mario at the entrance of Twilight Town, he appears by jumping out of the background, leaving a paperish hole in it. This effect also appears when Cortez's ship confronts Lord Crump's ship at the end of Chapter 5 and when Mario uses the Special Move Showstopper. Later in the game, when Doopliss is part of the Shadow Sirens, he actually has a problem as he is not able to vanish at one spot and appear at another, an ability used by Beldam and Marilyn. Doopliss has to smash a window in the Poshley Sanctum for himself only, and he always runs away alone when the Shadow Sirens have long since disappeared into the shadows, calling them to wait for him.
Doopliss's motives for his actions remain mainly unknown. According to himself, he turns the Twilight Towners into pigs because they are "depressing and boring and dimwitted all the time", and he thought that instead of wallowing in gloom, "they might as well wallow in mud". While this characteristic of Doopliss might be described as cruel, he is later portrayed childish, exclaiming "NO! NO! NO! NO!", "WHY? WHY WHY? WHY?", "HOW? HOW? HOW? HOW?" after Mario has guessed his name correctly. He frequently calls Mario and other people he does not consider friends "Slick", for unknown reasons. As a member of the Shadow Sirens, he suffers the same taunts as Vivian, but does not have enough power to resist them. Due to the fact that Doopliss changes sides after the game, teaming up with Flurrie, he may not be described as entirely "evil".
While impersonating Mario, Doopliss talks in a self-righteous manner. To Mario's partners, he says "All right, kids, put on your fighting gloves! Uh... Woo hoo! It's-a me!" He calls Vivian Mario's girlfriend, and after Vivian realizes Mario's true identity, Doopliss teases Mario with "See? Your friends ditch you because you don't have the charisma of me, Super Mario!". He also plays at Mario's popularity at the meeting with Mayor Dour, where the real Mario drops in and is not recognized by anyone else.
 Names in Other Languages