Protean Charm

The Protean Charm (incantation unknown) is a charm that links several objects together through a common purpose. The charm qualifies as Transfiguration in the Hogwarts School of Witchcraft and Wizardry curriculum.

In 1995, Hermione Granger used this charm to link fake coins in order to communicate with the members of Dumbledore's Army. The change in shape of one fake Galleon changed the shape of the others. Ravenclaw Terry Boot commented that the charm was N.E.W.T.-level and was very impressed by her ability to perform it as a fifth-year. Hermione explained she got the idea from the Dark Mark tattoos of the Death Eaters, which were used to summon them to their master. The coins were used constantly by various D.A. members until 1996. At that time, Ron Weasley and Hermione attempted to summon help during the Battle of the Department of Mysteries, but only Neville Longbottom and Luna Lovegood responded, as they were especially vigilant members.

The Protean-charmed Galleons were used once again in 1998 when the D.A. convened in the Room of Requirement to form a resistance against Headmaster Severus Snape and the Carrow professors. Hermione gave the master coin to Harry Potter, as he was the leader of Dumbledore's Army. Harry changed the date marked on his coin to reflect the next D.A. meeting time, which subsequently changed the date on the coins of all D.A members.

Draco Malfoy, inspired by Hermione's coins, used a similar method to communicate with Madam Rosmerta, whom he had under the Imperius Curse as part of his plan to assassinate Albus Dumbledore.

Etymology
The English word Protean derives from Proteus, a god in Greek Mythology. Proteus was a shape-shifter, able to take many forms. As a result, the word Protean has come to refer to versatility, flexibility, or an ability to assume many forms. "Protean" is also similar to "protein", derived from the same root, meaning a variable, flexible substance which forms strong bonds between its constituent parts.

Appearances

 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Deathly Hallows