How do u unlock the Bowser board and those two weird looking characters on Mario Party 8 for wii.

First u have to get up to Bowser's Warped Orbit in ster Battle Arena then u will VS Hammer bro. After that, u will have to get up to Bowser's Warped Orbit again and then u will VS Blooper. Try and beat him and then try and beat Bowser and then u will unlock him. Good Luck!

beat the ster battle arena once to unlock stage (bowser's warped orbit) and blooper to unlock hammer bro beat the ster battle arena twice.

Defeat ster Battle arena to unlock one of the unlockable characters, and then use the character u just unlocked to beat the ster Battle Arena again to get the other unlockable character.
(This response may be late but I'll say this for anyone else who needs help)

u have to go through all the party boards to unlock Bowser's board.And u get Hammer Bro if u go against him then u need to go against Blooper if u want to unlock him in Bowser's Party Board.