Dark Fawful Bomb
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.
The Dark Fawful Guys will appear with the Dark Fawful Bomb on top of the screen, waiting for an opportunity to drop the bomb onto Bowser. If Bowser uses his vacuum ability, he can swallow the Dark Fawful Guys, meaning that Mario & Luigi must battle them. As they are so high in the air, however (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 the other enemies, creating a giant purple explosion that will deal massive damage to them. 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.