A type of stock character that is used as a means of depicting a character's moral dilemmas. A shoulder devil is, most commonly, a small Demon Boy or Demon Girl appearing on a character's shoulder or beside their head to act as temptation and guide them towards the path of evil or mischief. They can be pictured as a smaller version of the character or as another character, usually but not always with added Demon Horns, Demon Wings, and a Demon Tail.
They are almost always accompanied by a Shoulder Angel on the character's opposite shoulder. A character can be marked as especially evil or mischievous by having another shoulder devil in the angel's place or by receiving similarly bad advice from both their shoulder angel and their shoulder devil.