Contest 2004 is a game where two spaceships fly around in an arena and fight each other an infinite amount of times, as the developer couldn't be bothered to program an ending for this one.
As with many Nice Code games, pressing Up, Down, Up, Left, Right, Left, B on the title screen will briefly display a credits screen. NCG stands for Nature Color Game, one of several aliases used by Nice Code, and PJ most likely refers to the Power Joy series of Famiclones which many Nice Code games have been released on.
An alternate version exists which replaces all of the graphics. The credits screen is still present, but because of the graphics being rearranged for this version it's now rendered out of 2's.
Spider Man 2
Another version loosely based on the movie of the same name was made and now features Spider-Man and Dr. Octopus fighting on the side of a building. The music was also changed for this version. Again, the credits screen is still intact and uses a different graphic tile for the ASCII art to the other versions.
Masked Man II
An alternate version of Spider Man 2 which changes the title screen and recolors Spider-Man's suit from red to yellow. However, the spider-themed HUD and Dr. Octopus' sprite are unchanged.