At first glance, Slap Fight MD is a direct conversion of the 1986 arcade classic Slap Fight from Toaplan and Taito, featuring a faithful conversion of the original title with several difficulty settings, as well as both original and arranged soundtracks. However, also included on the cartridge is a completely new sequel with all-new stages, bosses, graphics, and music. The basic gameplay is identical: a vertically-scrolling shooter where power-ups cycle through a list to choose from, and it is possible to construct massively-wide ships with incredible firepower. Slap Fight MD also adds the ability to jettison your ship's power-ups causing a massive screen-filling explosion that can potentially save your life.
Description from MobyGames