S.D.M.G.

The S.D.M.G is a straight upgrade to the Megashark, with the same fire rate and ammo usage bonus, except with a noticeably higher damage output. It also gives a +5% critical hit chance.

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.
 * S.D.M.G. is an acronym for Space Dolphin Machine Gun.
 * This item may also be a reference to Douglas Adam's book "The Hitchhiker's Guide to the Galaxy" where Dolphins are very intelligent beings capable of space travel, mostly because of the "It Came from the edge of Space" subtext.