Mushroom XIII is an enemy Heartless that is only found in Kingdom Hearts II Final Mix.
Although multiple Mushroom XIII battle you at the same time during the boss battle in Kingdom Hearts II Final Mix, they all look the same. First, they all have circular black heads, and you can only see their eyes due to the darkness of their hoods. They also all wear black zip-up coats with the Heartless emblem on the front of them, very similar to the ones worn by the members of Organization XIII with their hoods and pull-strings. The hood of this coat gives this Heartless its name, because it makes its head look like a mushroom. Also, similar to Organization XIII, each of these Heartless have a Roman Numeral from I to XIII on their back, representing the number rank they are. Each of these Heartless vary in size.