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. Dipper and Mabel try to find it with the aid of Soos on the S.S. Cool Dude. Dipper accidently finds the Gobblewonker which begins to chase them. The Gobblewonker then gets stuck in the hole of a cave. It is later learned that the Gobblewonker is actually a robot created by Old Man McGucket who likes to create extremely dangerous robots when he feels neglected or sad. However, the real Gobblewonker is shown at the bottom of the lake at the end of the episode and swallows the camera Dipper dropped.

Physical 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.

Also, compared to the robot, it was much less serpentine.

Voice
The Gobblewonker is voiced by Frank Welker.

Trivia

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