Doopliss

Doopliss hails from the Paper Mario series... more specifically from Paper Mario: The Thousand-Year Door.

Who is he?
Doopliss is a person who is ghost-like in appearance and has a special power which allows him to duplicate anyone he likes. This is special in the fact that when he does this he can steal not only their looks, but also their name as well. The person he duplicates then become a shadowy figure of themself and cannot be identified by their friends, family, or enemies (well except for Doopliss himself). This was first evidenced when Mario and his partners beat Doopliss for the first time. When Doopliss is beaten, Mario goes back to the new town he came from. Unknown to Mario's friends, this was not Mario but Doopliss disguised as him. The real Mario who looked like a shadow went back to the town but beforehe got there, he was ambushed by Doopliss Mario who told him that if he guessed his name that he would give Mario back his appearence and identity. If Mario guessed wrong he would face Doopliss in battle. Doopliss had an HP count of 40. Doopliss is into pranks as evidenced when Mario and friends got to the area he inhabited which was connected to a town ehich had an everlasting twilight over it. The area Doopliss was in was called Creepy Steeple. If you ended up battling Doopliss again, you had no other choice but to run away from the fight because now Mario's attacks were futile against him. When Mario got to the town he ran into one of the Shadow Sirens named Vivian who was looking for a Superbombomb. Once Mario found it for her she was thankful for him finding it for her that she joined him to get his identity back. Vivian had no idea who she was helping until the final time Mario faced Doopliss. When Mario guessed Doopliss's name wrong once again Mario still had no choice but to run away from the fight. When Mario and Vivian reached Creepy Steeple again they decided to find the person who knew Doopliss's real name. This "person" was actually a parrot. When Mario and Vivian reached Doopliss again, he asked them to guess his name. When inputting Doopliss, you must do it exactly like this: D-o-o-p-l-i-s-s, only without the little dashes. When Mario guessed Doopliss's name right he became upset and hid in the top tower of the Creepy Steeple yet again. This is where he was first fought. This battle however Doopliss was joined by Mario's friends except for Vivian. Doopliss's disguise managed to fool all of Mario's friends. However Mario knew this guy was a fake. Once Doopliss was defeated he became regular Doopliss again and fled.

Second sighting
Doopliss is later spotted again on a train headed for yet another of the Crystal Stars. Here he disguised himself as a celebrity named Zip Toad who threatened to yummify the train if he went to Poshley Heights, the location of one of the Crystal Stars. He had become a member of the Shadow Sirens at this point. Mario caught Doopliss before he could carry out the threat and when he did Doopliss attempted to flee and succeded when the train stopped to refuel.