S.D.M.G.

The S.D.M.G (Or Space Dolphin Machine Gun) is a straight upgrade to the Megashark, as well as a considerably close competitor with the Chain Gun, with a slightly faster firing rate and same ammo usage bonus, except with a noticeably higher damage output. It also gives a +5% critical hit chance.

The S.D.M.G. is currently unobtainable within the game, and the only way to get it is via an inventory editor.

Trivia

 * This item is a reference from the game Edge of Space (hence the subtext 'It came from the edge of space'), in which Terraria is also referenced or from A Hitchhiker's Guide to the Galaxy.
 * S.D.M.G. is an acronym for Space Dolphin Machine Gun.
 * Space Dolphins are a race of creatures in the DC Comics universe, favored by the character Lobo.
 * The sprite for this weapon resembles the Dolphins on the first edition cover of David Brin's novel Startide Rising. The Science Fiction novel features Dolphins genetically engineered for greater intelligence who wear harnesses with apparatus that allow them to manipulate objects.
 * Could also be a reference to the game, Ecco the Dolphin. In a notably difficult level, called Welcome to the Machine, Ecco enters 'The Machine' to fight an alien race and save his pod. Extensive use of the 'Death Sonar' is required for this level, and is a ranged attack( with S.D.M.G being a gun and all).