Flying Submarine
An actual flying submarine that started out in the original Party Goers. It belonged to MagiKoopa, but got stolen by Sapphire towards the end of the OG. Then there was two at one point in later OGs, I think, but one of em got blown up. It's really confusing as to which person actually had the still non-blown-up flying submarine, but both people had one, anyway. All in all, it was one of the reasons why MagiKoopa kept trying to write his characters out of the PGs (He held the belief that Sapphire's flying submarine was the one that blew up and she didn't have one). He put up a hell of a fight, though.
Also, if I can remember GORE's addition accurately, the flying submarine became a lot more common vehicle afterward and even inspired vehicles such as the Flying Monkey. Because of this, it caused Masa to be the subject of ridicule when he let the others know that his submarine could only go underwater in GMOG Holiday Special: Happy Father's Day Masa!.