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 initialism for Space Dolphin Machine Gun.