Master Miis are the hardest CPU Miis. These Miis are unlocked after winning a TV Party game against the Expert-level miis, but are always your partner in Balance Boat in Wii Party.
The other four CPU Skills are Beginner, Standard, Advanced and Expert.
List
Wii Party
Akira, Alisha, Asami, Eddy, Emma, George, Hiromasa, Jackie, Lucía, Marisa, Matt, Pablo, Pierre, Sakura, Steph, Stéphanie, Takumi, Tyrone, Víctor and Yoko.
Wii Party U
Araceli, Barry, Bo-Jia, Clara, Daisuke, Elena (Barbara in Wii Sports Club), Faustine, Jeff, Jianjun, Joana, John, Joost, Maximilian, Na-rae, Olga, Polly, Rie, Sara, Susie, William, Yuehua and Yuya.