I heard that for mario party 9 there was only these confirmed characters Mario Luigi Peach Daisy Yoshi Birdo Wario Waluigi Toad Koopa Shy guy
The source (see bottom) confirms bowsers minions are your 1 opponent every board on story mode; These are playable some point in the game as the source says Birdo Blooper Hammer Bro Koopa Kid Shy Guy Koopa Boo Dry Bones
So my prediction
Starting Mario Luigi Peach Daisy Yoshi DK Toad Toadette Wario Waluigi Rosalina* Diddy*
Unlockable Boo Birdo Dry Bones Hammer Bro Blooper Koopa Kid Shy Guy* Koopa*
- means new
Why these: Because I wanted to new goodies and two new baddies Diddy Dk pair Toad and Toadette pair Yoshi and Birdo pair Rosalina will pair with Lubba (downloadable) Koopa Kid will pair with Kamek (downloadable)
Let's hope this could be true but remember the source only Said these Will b playable; Mario Luigi Peach Daisy Toad Yoshi Wario Waluigi Birdo Boo Koopa Kid Dry Bones Hammer Bro Blooper Koopa Shy Guy
The others (Dk Rosalina ect.) we're my prediction but if My pred is wrong it will be one pot left probably Dk or Toadette.