You are able to play the Fantasy Adventure II in the living room in your house to the right with a TV and video game console in front of it. You should be able to play this game when you start the game.
Click on the console with
. Then load into the game. Once you do collect the 3 coins and then walk into the castle. You must select the book to the right in order to kill everything. In the next room attack with
and kill the two skeletons and the vampire before exiting the level.
That's it you beat the game ad unlock the achievement.