From the Super Mario Wiki
Dark Fawful Bombs are enemies that appear in Mario & Luigi: Bowser's Inside Story. They are huge, purple Bob-ombs with an imprinted black star on their face and a lit fuse. They rarely appear, but when they do, they always appear alongside two Dark Fawful Guys that carry them. They only appear in battles where at least one Naplock or Dark Trashure was present at the start, but not if any Dark Mechawfuls were in the battle.
They appear on top of the screen, waiting for an opportunity to drop the bomb on Bowser. If Bowser uses his vacuum ability, he can swallow the Dark Fawful Guys, meaning that Mario & Luigi must battle them. But since they are so high in the air (they are seen on the upper screen and not the touch screen), the player must rapidly press many times in a row. Without the Dark Fawful Guys supporting the weight of the Dark Fawful Bomb, it will land on all the enemies, creating a giant purple explosion that will deal massive damage to all the enemies. If Bowser does not suck the Dark Fawful Guys in after a few turns they will drop the Dark Fawful Bomb on him and cause massive damage.
- Dark Fawful Bombs are quite similar to Shroob-ombs from Mario and Luigi: Partners in Time, as they both are larger than normal Bob-ombs, both are purple, and both appear with enemies who carry them. As Mario and Luigi: Bowser's Inside Story is the sequel to Mario & Luigi: Partners in Time, it may be possible that the Dark Fawful Bombs are based off Shroob-ombs.
- ^ Prima's Official Premiere Edition game guide to Mario & Luigi: Bowser's Inside Story (approved by Nintendo)