It's appearance varies by episode. In some episodes it is normal looking, but with a glowing aura or green. In others it is covered in skulls and various symbols.
In Billy and Mandy vs. the Martians, it's revealed that there is a large portal on the inside, explaining the large number of contents.
|Spider Egg||The Crawling Niceness|
|Evil Powder||Brown Evil|
|Voodoo dolls of Billy and Mandy||Brown Evil|
|Fancy Jake||Billy and Mandy vs. the Martians|
|Phone of Cthulu||Prank Call of Cthulu|
|Merlins Underwear||Billy and Mandy vs. the Martians|
|Holy Grail||Billy and Mandy vs. the Martians|
|Monster Manual Volume 1|