Much referenced but never actually seen is the original ad Roberta and Ken Williams took out as On-Line Systems for Hi-Res Adventure: Mystery House, in the May 1980 issue of MICRO: The 6502 Journal. The 6502 was the microprocessor used in the Apple II, which was the machine On-Line initially produced all their products for during their first couple years in operation in the early 80s.
While some sources claim it was a quarter page ad, we can clearly see that it was a full-page piece. From the extensive text to the prices to the almost entirely unknown two other arcade games sold alongside Mystery House (Skeetshoot and Trapshoot), there's lots to chew on here. I'm not one for "Holy Grails" of game history, but...I must admit to certain fascination with this ad. It's a pleasure to put this back in circulation.