Gobblewonker

The Gobblewonker is a legendary sea monster that is thought to live at the bottom of Lake Gravity Falls. In the episode, "The Legend of the Gobblewonker," Dipper and Mabel embark on a mission to get proof of the legendary sea monster that lives at the bottom of the local lake, to win a photo contest.

History
When Grunkle Stan takes Dipper and Mabel to the lake for some "family bonding time," Old Man McGucket starts running around the pier saying he had seen the Gobblewonker. It is later learned that the Gobblewonker is actually a robot, and Old Man McGucket creates extremely dangerous and destructive robots when he feels neglected or sad. However, the real sea monster is shown at the bottom of the lake at the end of the episode, which promptly swallows Dipper's last camera as the episode ends.

In "Headhunters," a part of the Gobblewonker can be seen as scrap metal behind Old Man McGucket in the Car Graveyard.

Appearance
The Gobblewonker was described by Old Man McGucket as having a long neck like a giraffe, and wrinkly skin like Grunkle Stan. The real Gobblewonker at the end of the episode had green, scaly skin. It's eyes were dark green and its lower jaw overlapped its upper jaw. It had two tusks along with other sharp teeth, and its head had two fish hooks stuck in it, one on its nostril, and one just above its eye. It had short legs with webbed feet and its tail had a fin like a fish. Its back had a long mane like a horse's that ran down its back.

Trivia

 * The Gobblewonker is based off the many legendary lake monsters often reported by eyewitnesses in several countries but never proven, such as the Loch Ness Monster and the Ogopogo.
 * The roars and growls that the robot Gobblewonker made were the same as the Tyrannosaurus Rex from Jurassic Park.