From the Super Mario Wiki, the Mario encyclopedia
In The Super Mario Bros. Super Show! episode "Rolling Down the River", Captain Koopa uses the Sinister Star to race against Mark Twang and his ship, the Ding Bell for the status as "King of the River" (and presumably, the rest of the River World). Captain Koopa had also held the captured Toad and Princess Toadstool aboard the Sinister Star.
The Sinister Star was apparently destroyed when Princess Toadstool, having gained control of the Sinister Star's steering wheel, crashed it into a beach.
The Sinister Star was quite large in size, having several floors and rooms, including prisoner cells and possibly a kitchen. The Sinister Star was also crewed by various Koopa Troopas and Goombas, with First Mate Mouser as the ship's second-in-command; Clawgrip was also, apparently, the driver of the Sinister Star.