Shadow the Hedgehog is one of the few beings that has any sort of power over the Tails Doll.
Shadow was created by Dr. Gerald Robotnik, grandfather of Dr. Ivo Robotnik. He was made to be the Ultimate Life Form, using the DNA of Black Doom. The project was shut down by GUN, and Shadow was locked away for 50 years, before being brought back to life by Dr. Robotnik. Shadow worked under Dr. Robotnik while trying to figure out his past, being amnesiac. Despite being evil throughout the game, he fought against the final boss Biolizard after changing alliances, eventually sacrificing himself to save all of humanity.
Though he supposedly died, it was revealed he was actually very much alive during the events of Sonic Heroes, but just hidden and unconscious in the basement of one of Robotnik's bases. Still searching for his memory and purpose, he teamed up with Rouge the Bat and E-123 Omega to find answers.
The Tails Doll is said to have a sort of fear of Shadow. The video game Shadow the Hedgehog is said to be able to ward off the Tails Doll, but any image of Shadow is suitable for this purpose.
Shadow looks like a black hedgehog, with quills spiked up. He has red stripes on his quills and his grey chest hair is fluffed up.
- Shadow was conceived to be the direct opposite of Sonic, to represent the dichotomy of good and evil as the theme for Sonic Adventure 2.