Mark Johns is chasing a ghost. This is what he tells me. It’s not quite the truth. The spectral quality of this “ghost” isn’t immateriality; interfacing with it isn’t a problem, Johns has done that thousands of times. The hard bit, and the bit he’s after, is understanding it. The ghost is actually Spelunky: a procedurally generated action-platformer that Johns declares “might be the greatest videogame ever made.” But Johns reaches for metaphor, as he’s the kind of guy to give into the lure of theatrics if given the chance. He lives in the moment. Snatch him a boiler suit and…