Emerald Mine (1987)

A conversion of the classic Boulder Dash game. The player is deep down in a cave and have to collect emeralds and diamonds while evading monsters - and the laws of gravity, which have the annoying habit of squishing him with huge rocks if he happens to stand beneath one as it falls down. The game also has a two-player mode where two people can rid caves of their valuables at the same time - in addition to the 80 levels, there are 20 exclusive two-player levels.