Dolphin was a member of The Original Smoosh who served Nintendoki 2000 before the formation of the Smoosh we know today. Not much is known of this mysterious character, except for the fact that his weapon of choice was apparently a Magnum with dragon patterns painted on the side. Like the other Original Smoosh members, Dolphin was somehow sent to a parallel Universe, and, although he hasn't been seen, it is implied that he is still alive.
In Luna's flashback, Dolphin was seen invading Luna's Homeworld along with the rest of the Original Smoosh in search of the Miracle Thread. Upon encountering Luna and Sola, Dolphin threatened them in an attempt to obtain information about the whereabouts of the Thread, but was interrupted when Link showed up, announcing that he had been sent by Princess Zelda to protect the Royal Family of this World. Dolphin and Link then proceeded to fight. The outcome of this battle is unknown, but it may have resulted in Dolphin's exile from The Universe.