Are you certain that it's Super Mario Brother's 3 you're thinking about? I don't really remember that line in the game at all, let alone a koopa kid talking...But I will confess it's been awhile since I played Mario 3.
The secret weapon could be referring to his army of tanks in the Dark World, or his super fast airship, or his...Evil boat thing in the dark world. I guess I really don't know.
Kweeh! Forget Whark! Kweeh! Is better!