From the Super Mario Wiki
Goombetty is a female Galoomba.
She appears in the game Mario Party Advance as Goombob's crush. One of the game's missions involves finding a seashell for Goombob to give her. After Goombob givers her the shell the player collects, Goombetty arrives at the manor, and Goombob gives her the shell and asks her on a date. Goombetty accepts, and leaves to prepare. The ending of the game says that Goombetty loves Goombob madly, and she has made a hobby of collecting seashells.