Cursed barrier

This curse was used by an unknown Death Eater during the fight against Order of the Phoenix around Hogwarts' Astronomy Tower. It was used to prevent the members of the Order from interfering with Draco Malfoy's attempt to assassinate Albus Dumbledore.

The curse creates a barrier around a certain area, preventing anyone from passing through it, throwing them backwards on contact. Only Death Eaters with a Dark Mark on the arm can go straight through it as though it is not there. If the area around the barrier collapses, the barrier would be dispelled.

Severus Snape, though a loyal member to the Order of the Phonenix, was able to go straight through only because he bares the Dark Mark.

Behind the scene

 * Since the Dark Mark was invented by Lord Voldemort, it is likely that this curse, compatible with the Dark Mark, is also one of his inventions.