Danger Bridge is a surprisingly decent ripoff of the Game & Watch Manhole game.
As with many Nice Code games, pressing Up, Down, Up, Left, Right, Left, B on the title screen will briefly display a credits screen. (Note that it only works after the title screen fades in) Nature Color Game is 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.
A variant of this game exists which replaces the graphics. The intro and title animation were removed and the code to access the credits screen was disabled.