Doopliss

In Paper Mario: The Thousand-Year Door, Doopliss is a Duplighost who has been causing trouble at Twilight Town, turning everyone into pigs and stealing Mario's identity and teammates, leaving Mario his shadow, also getting Mario hunted down by an angry mob. His base of operations is Creepy Steeple. To find out what his name was, the player had to find the Superbombomb and give it to Shadow Siren Vivian. Vivian will join the team and Mario and Vivian had to do the same thing the characters did in Rumpelstiltskin: guess Doopliss' name. The only thing Mario and Vivian were missing was the lower-case letter P. After getting the letter P, they guess Doopliss' name and Doopliss flees back to Creepy Steeple. While battling Doopliss, Vivian discovers she joined Mario's team and she does a little time to think it over and joins the team for real, because Mario treated her a lot nicer than Beldam and/or Marilyn. Upon defeat, Doopliss surrenders Mario's identity and teammates back to Mario and gives Mario the Crystal Star he deserves. He flees Creepy Steeple in humiliation and joins the Shadow Sirens for revenge. He becomes a lot nicer at the end of the game and pursues a career in acting alongside Flurrie.

Paper Mario 2 Stats
Creepy Steeple Battle

HP 40, Attack 4, Defense 0

Tattle: ...??? Wow, hoe totally bizarre... This thing isn't here. There's a monster in here that looks like this thing... But it doesn't have a name. It's apparently good at transforming itself and other things. Maybe it used that power to tun the villagers into pigs! This thing is a real jerk!

Palace of Shadow Battle

HP 40, Attack 6, Defense 0

Tattle: That's Doopliss. He's a shapeshifter, and even turned into you once, Mario! He may turn into one of us and attack. When he does, he'll have our abilities! Hey, how do you think he became one of the Shadow Sirens? Isn't that...weird? How do you think he stands Beldam's abuse? You think he's all right in the head?