This game was originally implemented in Game Maker by Daniel Remar. This is the GNU/Linux implementation by Andreas Remar. The Windows version can be found at Daniel's base. As I've lost interest in the project you are most welcome to pick up the source and complete the few small things that are left to do (see the retro.org file in the doc dir).
Retrobattle is made to look and feel like the classic arcade-style NES games, such as Ice Climber and Clu Clu Land. Not only are the sprites limited to three colors each, but the scoring, increasing difficulty, and setup of the game makes for a challenging arcade experience that mixes various oldschool concepts. Note that playing on Skill 1 is pretty boring compared to the havoc of Skill 8, so it may seem slow at first.
Use git to fetch the sources you need.
You may also want to try the level editor.
To compile you will need SDL and SDL_mixer development packages.
The data files are currently located in a hardcoded path from where the executable is located, i.e. in the parent directory. So if the executable is located in /path/to/retro/src/ then graphics will be searched for in /path/to/retro/gfx/. Relocatable data files is of course in the TODO. Running from the source directory (src) is recommended.