Vivian

Vivian is Mario's fifth party member in Paper Mario: The Thousand Year Door.

At first, Vivian is one of the Shadow Sirens. They battle Mario in Boggly Woods for Flurrie's necklace in Chapter 2.

However, at Creepy Steeple, Mario fights Doopliss, a Duplighost. He steals Mario's body and identity, leaving Mario as a shadow.

When Mario returns to Twilight Town, he finds Vivian searching for a Superbombomb. Mario finds it for her and Vivian asks him what he is doing here. Mario tells her about Doopliss and Vivian agrees to help get his body back.

When Mario and Vivian finally reach Doopliss' room in Creepy Steeple again, they battle him along with all Mario's old partners, who think Doopliss is Mario. Vivian realises that the one she was helping was Mario, but she joins him anyway because Mario was much kinder to her than Marilyn or Beldam. At the very end of Mario's adventure, Beldam and Marilyn end their villain activites and promise not to mistreat her again.

Outside of battle, she possesses the same ability Lady Bow has in Paper Mario, in which she hides Mario and his team in the ground.

It is interesting to note that in the japanese version of Paper Mario: The Thousand Year Door Vivian was a boy.

In a rough translation of the character description of Vivian:

"One of the shadow group, Vivian appears to be a girl but is really a boy."

Also in a rough translation Goombella's Tattle of Vivian:

"That's Vivian. Of the shadow group, she's the youngest sister... er, brother."

Attacks

 * Shade Fist (0 FP)
 * Veil (1 FP)
 * Fiery Jinx (6 FP)
 * Infatuate (4 FP)

Stats (when she is an enemy to Mario)
HP: 10, Attack: 1, Defense: 0