An "Invincibility Coke", also known as the "invisibility cloke" is an item that belonged to Vampire and to Ebony. It is described as being black and large enough to fit at least three people underneath it. Ebony and Vampire use one to avoid detection by Mr. Norris in Chapter 21, although Filth is still able to find them whilst concealed under it. In Chapter 29, Ebony uses her own cloak so that she, Vampire and Draco can sneak out of Lucian and Sirius' party.
It appears to be based of the Invisibility Cloak of canon, although the two differ: whilst the invisibility cloak makes the wearer invisible, the Invincibility Coke remains visible at all times.