|This article contains canon information corresponding to the Tales of Arcadia franchise. That means all information in this article is true and has appeared/been validated officially on-screen.|
Gaggletacks are magical, horseshoe-shaped totems that can reveal a Changeling's true form.
In "To Catch A Changeling", after failing to prove to Vendel that Bular is rebuilding the Killahead Bridge and that Changelings are dwelling in Arcadia, Jim suggests they find another changeling to prove that Nomura isn't working alone. Blinky takes Jim and Toby to RotGut's, where they receive a Gaggletack to reveal a changeling.
Jim and Toby try to use the Gaggletack on the faculty and students in their school, but each one came out clean. Toby then attempted to use it on Strickler, though he tricks Claire into returning it to Jim. Toby then tries to use it on his dentist, but it doesn't work. Instead, it was actually his dental hygienist, Gladys Groe, who was the Changeling. When Blinky and AAARRRGGHH!!! arrive to fight Gladys, she accidentally grabs the Gaggletack, which reverts her to her true troll form.
Later, in "Adventures in Trollsitting", believing that Claire's brother, Enrique, has been swapped by a Changeling, he volunteers to babysit while bringing a Gaggletack to be sure. However, he realized that the baby imposter hid it from him. So, he calls Toby to bring in a second (by buying it with an argyle sock). Jim then uses the Gaggletack to reveal that Enrique was actually NotEnrique.
Gaggletacks are basically horseshoes made of pure iron.
Gaggletacks are artifacts of great mystery. With physical contact, they reveal the true natures/forms of a Changeling, like turning them to their troll forms if their in human form and vice versa.
Gaggletacks must make complete physical contact with the Changeling in order to force them to switch into a different form. If a changeling handles a gaggletack with a piece of cloth, like what Gladys Groe did in "To Catch A Changeling", it will have no such effect on them.