Riptide, a glider sea pony, is tasked to to travel to the mainland and find Princess Celestia on behalf of the sea ponies, who fear their possible extinction. Once on land, he'll have to travel the tiny land of Equestria, make his way to Canterlot, (just a few hours from the coast, or so he's been told) and deal with the local wildlife, terrifying pony gobbling monsters like possums and hedgehogs. (Which Riptide imagines to be some kind of porcine-plant based horror.)
Selected because Celestia sent a message requesting a pony that needs to make friends, Riptide suffers from crippling social anxiety disorder. He carries with him the hope of the sea ponies.