I just picked this up tonight: a screen-matched Bob-omb from Super Mario Bros. Its provenance is stellar, as the prop comes straight from a crewmember who worked on the film. He was nice enough to share some more information with me.
This exact Bob-omb can be seen when the fungus offers it to Luigi (John Leguizamo). The mono-filament attached at the top used to be covered in slimy fungus and was used to lower the Bob-omb to Luigi in that particular scene.
"Hey, look at that! What is that?" Luigi asks Mario (Bob Hoskins) as the Bob-omb appears. When Luigi reaches for it, Mario pulls him away and shouts, "Goombas! Let's go!"
This prop is actually a modified TOMY wind-up walking toy hand-painted in matte gray (the Reebok logo on the soles of the Bob-omb would have covered the TOMY copyright). The winding key was added to the prop and is no longer present because it was made of paper and did not withstand after filming. In fact, the paper-made keys did not last long on any of the several Bob-ombs used in the movie.
The Bob-ombs, themselves, were also fragile, so it is unknown how many of these have actually survived.
See the attached photos.
"Trust the fungus!"