Ryuk

Ryuk is a Shishigama (a death god or grim reaper) from Death Note. While he acts as a sidekick and advisor for the protagonist Light Yagami, he was the demon that gave Light his iconic Death Note.

Shishigami

 * Immune to any form of physical harm
 * Invisible to humans (unless they show themselves)
 * Can see the names of humans as well as their lifespand.
 * This guarantees that Shishigami can write their victim's name without mistake.

Death Note

 * Notebook of the Shinigami
 * Used by these demons to feed on human lifespands to extend their own lives.
 * The book is magically imbued to kill any human who's name is written in it.
 * The death will occur automatically within 40 seconds as a heart attack (or if the details of the death are explained, it will take 6 minutes and 40 seconds; unless the time of death is listed).
 * Ryuk can determine the details and time of the death.
 * Cause and time of death must be within reason
 * Can manipulate peoples actions before death; brainwashing them to commit suicide.
 * Can kill multiple people simultaneous from the same event that killed them; so long as it is physically possible.
 * The book will create an infinite amount of pages to guarantee that it will never run out.
 * Scraps of Death Note work as well as the book itself
 * Any mortal human killed by the Death Note cannot be revived under any condition.

Feats

 * Killed Light.