Duplighost

Duplighosts are ghost-like creatures that can take on the appearance, voice and abilities of other people. They first appeared in Paper Mario, and a single Duplighost was later featured in the sequel, Paper Mario: The Thousand-Year Door. To attack, Duplighosts can either fly into Mario, or turn into his partner. In partner form, a Duplighost's attacks are weaker, and changing takes up a move, giving Mario a better chance at winning the battle.

Paper Mario
A Duplighost was first seen in Paper Mario at the Toad Town Dojo, where Mario fought a blue-sheeted Duplighost named Lee. More Duplighosts appeared in Chapter 7, in the Crystal Palace, where they used the mirrors in the palace to confuse Mario, as the reflections make it tricky to determine whether a character is the real thing or a Duplighost. Also in Chapter 7, one Duplighost pretends to be Kooper, and Mario must hammer the imposter to proceed. Likewise, in the Crystal Palace, four Duplighosts pretend to be Bombette and must also be hammered to proceed. Finally, also in the Crystal Palace, four Duplighosts pretend to be Kooper but instead dress up as Luigi, Goompa, the Koopa Koot, and Kolorado. Another Duplighost appears in Bowser's Castle, trying to trick Mario into believing he is Princess Peach. Mario can break the Duplighost's disguise by hammering the fake princess repeatedly.

Paper Mario: The Thousand-Year Door
Paper Mario: The Thousand-Year Door has only one duplighost, Doopliss, who stays in the Creepy Steeple. Many of the Twilighters refer to him as a demon since they have never seen him in person. In the game, Doopliss appears as an enemy of Mario several times throughout, 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 and succeeds for a little bit. 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. He still has the same powers and abilities as regular duplighosts such as throwing himself at people and most importantly, transforming into others to take physical appearance and attacks.

Profiles and statistics
If a Duplighost disguises as Goombario and uses Tattle, he'll say:
 * "It's Mario, silly! He's here to save Princess Peach, who was captured by Bowser. Remember? He fights until the bitter end, no matter what enemies attack."

Trivia

 * The name "Duplighost" is a portmanteau of the words "duplicate," which means to make copies of, and "ghost."
 * If the enemy copies Lady Bow, and the player has the Defend Plus Badge on, the enemy cannot damage Mario.
 * Oddly, electrical sparks are not seen coming from the Duplighost mirror version of Watt, but when the mirror is underneath her, it does.
 * Even if the two Duplighosts in Crystal Palace are defeated by Mario's partner, they'll still say, "Noo!! The real Mario 's so strong!"
 * In Japanese version, they talk in various Japanese dialects after defeated.