The game in question is an old-school text adventure called Hadean Lands.
Like so many of those classic titles from yesteryear, there are no graphics in the game; you simply type in commands and read the story of an apprentice alchemist stranded on an alien planet.
As you can imagine, the game is pretty hard, and it s this difficulty that led to developer Andrew Plotkin adding the unique piece of DLC to Steam.
Your $35 gets you a file containing a printable PDF or JPEG certificate, which states that you pledge to complete the game without using walkthroughs or referring to any hints.
Speaking from a player's point of view, he said: If this was a $5 game I d just close the game window, but after paying $30 I want to kick its butt.
And it should come as little surprise to learn that he s already sold at least one of the certificates so far.