Kid Icarus/WMG

3DS Wild Mass Guesses Go Here

Pit used to be a full god, who was killed/injured by Medusa.
Possibly a counterpart with Palutena. This is why he can't fly for long without help; his wings are actually crippled. The Non-Canon "Best Ending" in the first game was his true form.
 * He doesn't remember; either due to trauma or Palutena induced it out of compassion.
 * Maybe Pit was the god of love, their version of Cupid.

Pit is the last of his kind.
When Medusa's army invaded Skyworld in the first game, it's likely that all the angels that could went out to fight and defend their home. The monsters defeated/killed most of them. The rest were captured, but died in captivity in the Underworld. Pit survived captivity, and through a bit of magical aid from Palutena and leveling up, was able to return to Skyworld. We haven't seen any signs of other angels in recent media, implying that he might be the only one that made it out of the Medusa disaster alive.
 * I've thought the same thing, but he has a dark side/version (probably evil) in the multiplayer at least, so he can't be the last of his kind unless he and "Dark Pit" are considered to be the same person. Also, it's possible the Centurions are supposed to be angels, just in this universe they only have wings if high ranked or something.
 * Maybe not the last of his kind but if the only other angel left is a copy of Pit, it doesn't bode well for the angel gene pool even if males can somehow produce non clone offspring. It is called Angel Land though, at one point the Underworld, Overworld and Skyworld could have all been populated by angels. Maybe there was a greater cataclysm in the past, that allowed humans, gods and monsters to slowly start taking their places before the Medusa incident finished them off for good.
 * But what about the angel feathers Pit can find? They imply that at least part of the angels don't decompose, so there should be enough genetic material around to truly revive the angel species once someone gets some cloning technology that is both reliable and affordable.

Of Myth And Monsters was not a sequel to the first game.
It was a prequel. It wouldn't make sense for Pit to need training for the items he used to save Angel Land already, so it had to be a prequel. The reason the Armor wasn't counted as one of the three treasures in the first game is because it was never lost, Pit decided not to don it until he got the Wings Of Pegasus because it would be too heavy without them. The Mirror Shield is a part of the set he didn't use last time, so there were still three to get.

Look at the Komaytos. In the first game, they look just like Metroids but don't act like them; in Of Myth And Monsters they look less like Metroids, only having one tooth and one internal nuclei. Now in Uprising, they are Metroids in everything but name; this is because over the three games they were adjusting to a new planet, and as they are the least developed in the Game Boy game it has to be the first chronologically.

This is also why Medusa was able to conquer Angel Land. Palutena was still recovering from her encounter with evil king Orcos, and Pit fell into the underworld after the sun burnt his wings; he had in fact been there long before Medusa came out and her leading the underworld troops against overworld and skyworld is what let Pit escape, as they otherwise would be too busy guarding Pit, preventing him from getting a weapon. Uprising is the first true sequel and is going to show us that Medusa will not be able to get nearly as far when both Palutena and Pit are at full strength.