Kryptos

Kryptos is a character in Gravity Falls, appearing in the episode "Weirdmageddon Part 1." He is an old friend of Bill Cipher and part of the Gang of Interdimensional Criminals and Nightmares. He, along with Bill and the rest of the gang, was trapped in a decaying dimension, but was finally set free when the rift between the dimensions cracked during the prophesied Weirdmageddon.

History
Kryptos has unknown criminal history.

He was prisoner of a dimension for trillion of years craving to leave it and have fun at last.

Season 2
In "The Last Mabelcorn" Kryptos can be heard cackling and cheering in Ford's flashback, inside of his dream dimension, through a rip made by Bill, as the latter reveals his true intentions.

In "Weirdmageddon Part 1" he is finally set free from his dimensional prison and stands along with the rest of the gang until the party starts.

Inside the pyramid, in the heat of the party, he can be seen dancing and drinking with the other demons, and when the Time Police crashes the party and the Time Baby is vaporized, he is worried, but the worry turns to malicious excitement, as the party gets on.

Appearance
Kryptos is very similar to Bill, as in he is also a floating shape with black limbs. However, he is a navy rhombus, and the top perimeter of his shape resembles a compass, with a functioning eye at the turning point, and the bottom perimeter resembles a square ruler. Additionally, he has a big wide mouth with buck teeth and wears black gloves.