Brent Green

Brent Green (AKA "The Invisible Boy") is the main villain in the Goosebumps book, My Best Friend is Invisible.

History
He was initially thought to be an invisible ghost by Sammy, the protagonist, but in the twist ending it's revealed that he's actually a living, human boy who was somehow made invisible by his mother, so he would survive in a world now inhabited by aliens (including Sammy and his family).

Television
Brent Green appeared in the television adaption of My Best Friend is Invisible, portrayed by Darcy Weir. At the end of the episode, Sammy and his parents surround Brent menacingly, possibly with the intent of killing him.

Film
Brent Green appears in the 2015 Goosebumps film voiced by Jack Black, but referred to and credited as the Invisible Boy. He suddenly appears on the the windshield to R.L. Stine's car leaving noticeable hand prints. He climbs around the car and hits Champ in the face. Stine removes him by accelerating the car really fast then comes to an immediate stop flinging him from the car. He replies by shouting "Not cool!".

At the end of the film, he reveals to Stine that he somehow evaded getting captured by typing "The Invisible Boy's Revenge" on his typewriter and leaves hand prints on the trophy case as he quotes "You forgot about me!". Stine screams in horror as Brent's hand print appears on the cabinet glass while Brent maniacally laughs. The image is then turned into a book cover with the tagline "Invisible but deadly."

Some see the Invisible Boy not getting sucked up by the book as a plot hole, due to Zach Cooper writing "all the monsters go back into the book." However, there are some theories to combat this:
 * A possible reason the Invisible Boy was at the end of the movie and not in the book was possibly because he was "out of range" when he fell off Stine's car, he was likely still out there when he was dropped thus he was too far for the book to absorb him.
 * Another, more plausible reason for the invisible boy not having been sucked into the book was because he was too far away and needed more time to be sucked in before the book was closed.
 * Another possibility is that Brent, who is in fact, a human boy, was excluded as Zach stated in the movie that only "monsters" were to be sucked into the book. Because Brent is not a monster, but a human turned invisible, he would have not been sucked into the book.
 * Another possibility is that since Stine said for the monsters to be sucked back in, he would have to write a "real Goosebumps story," which almost always includes a cliffhanger, at least one monster would have to be left behind for it to work.

Quotes

 * "NOT COOL!"- Goosebumps (2015 film)
 * "You forgot about me!"- Goosebumps (2015 film)