The Shadow Glob is a Pureblood Heartless that is found in Kingdom Hearts and Kingdom Hearts 358/2 Days. It is an immobile, black-violet orb of darkness. While it does appear in Kingdom Hearts, it is unnamed, and is only given a name and journal entry in Kingdom Hearts 358/2 Days.
After Oogie Boogie is defeated, his darkness, in the form of Shadow Globs, brings him back to life by fusing the villain with his manor as a giant monster. However, Sora, Donald, Goofy, and Jack Skellington manage to put him down for good by destroying the Shadow Globs that were animating him.
According to the data Saïx provides Roxas, Shadow Globs are naturally occurring dark masses that attract Pureblood Heartless. However, they only appear in worlds where the Heartless have already infiltrated.
Twilight Town, Beast's Castle, Agrabah, Neverland, Wonderland, and Halloween Town each suffer at least one infestation of Shadow Globs during Roxas's time in the Organization. Roxas is sent to get rid of them, in order to restore the emblem Heartless quality for heart collection.
This information is based on alternate scenes or materials and is not considered canon within the overall plot of the series.
In the manga, the Queen of Hearts constructs castle out of Shadow Globs. However, Roxas destroys it. A temporarily giant Luxord replaces the castle with one of made cards.