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. It currently cannot be obtained legitimately in the game, but Redigit stated that it will be added in the update along with the Lunar Boss.

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.
 * The item also appears to, unintentional or not, a reference to "The hitchhiker's guide to the galaxy", as at the end of the radio series it is revealed that all the dolphins went to the end of the universe.
 * S.D.M.G. is an initialism for Space Dolphin Machine Gun.
 * The acronym "S.D.M.G" is similar to the acronym "S.M.G", which stands for Sub-Machine Gun.