Tails Doll is a character from Sonic R, who became the basis of various Creepypasta stories due to his unnerving nature. In Sonic R, Dr. Robotnik created Tails Doll as a robotic counterpart to Tails (much like Metal Sonic) in order to compete in races against him. In his many creepypasta stories, however, he is a demonic entity who kills anyone that performs the “Tails Doll Curse”.

More facts here: https://fridaynightfunking.fandom.com/wiki/Vs._Sonic.Exe#undefined