Steve Argyle - Ghosts of Dragonspear Castle
Legion of Avernus Hobgoblin
Ghosts of Dragonspear Castle was a GenCon 2013 exclusive paperback for D&D Next, the official name for the 5th Edition of Dungeons & Dragons. Copies of the book sell for $100 or more these days.
Steve Argyle has a piece on page 244 of the book, shown above, which Steve calls “Legion of Avernus Hobgoblin”, that was originally seen in Dungeon Masters Guide 2 from September 2009.