The Crystal Flashlight is a red flashlight with a height-altering crystal attached to it, when fired, can grow or shrink the desired target. It features most heavily in the Gravity Falls episode "Little Dipper".
Background
Physical description
The flashlight is red with a pink bar around the button that turns on and off the flashlight. The crystal is attached with a band that connects to the ends of the crystal, and attaches to the handle of the flashlight with tape.
Usage
To use the crystal flashlight, one must turn the crystal attached to the lens to the side so that it causes the target to grow or shrink. By pressing the light button, the flashlight fires a beam, light blue for a size increase and pink for a size reduction, and will cause the subject to grow or shrink, with a more drastic change occurring the longer the button is held down. When the desired size is reached, the user must let go of the button.
Role in the series
The twins fight over the flashlight.
After Mabel Pines incessantly teases Dipper Pines about being taller than him, nonetheless by a mere millimeter, the latter becomes jealous and seeks out a way to grow himself to equal height. After reading about a strange size-changing property hidden in the Gravity Falls forest in 3, Dipper sets out to find said property, which he learns to be crystals, and uses one to assemble a device to make himself taller. After he shows his sister that they are again the same height, she argues that, since her growth spurt occurred first, she would be taller in the end, and proceeds to mock him again. Dipper, angered, uses the flashlight a second time to become taller than Mabel, who, when she sees her brother, learns of the flashlight and fights over it with Dipper, ultimately resulting in Li'l Gideon getting hold of it and uses it to shrink the twins. Gideon takes them back to his house and interrogates them as to how they came upon the magical item.
Gideon prepares to shrink Stan.
After a failed attempt at blackmailing Grunkle Stan into giving him the Mystery Shack, Gideon decides to shrink Stan and take the Shack and makes his way to the location, with the twins following close behind in hopes of stopping him. Dipper and Mabel nearly manage to return to normal size but are caught in the midst of their bickering. Gideon enters the Shack and fires the light at whom he thinks is Stan, but is actually Soos. When Soos accidentally divulges Stan's location to Gideon, the boy approaches Stan, and, after learning Stan is in a maze of mirrors, uses the flashlight to smash the mirrors to help him navigate. As Gideon is about to reduce his enemy's size, the twins manage to stop him by tickling his armpit. Grunkle Stan then rolls Gideon out the door, and Dipper and Mabel use the light, which was left behind, to regrow each other back to normal size with a grateful Dipper allowing Mabel to retain her extra millimeter. They then destroy the device, but when they realized that they forgot to regrow Soos to normal size, they attempted to fix the flashlight with "lots of glue".
In the series finale "Weirdmageddon Part 3: Take Back the Falls" the flashlight is used while the team are work to build the Shacktron and later when the Twins try to escape from Bill, however it was never mentioned whether if this was the someone or if it was another flashlight they made.
