The 404 Demon is a MYTHICAL pet that is obtainable from the Hacker Egg. It is based on the 404 error for websites and the pet makes glitching sound effects in the game.
The latest Pet Simulator X value list for 404 Demon can be found below:
💎 13,100,000 (13.1m)
💎 27,100,000 (27.1m)
💎 256,900,000 (256.9m)
💎 1,000,000,000 (1b)