When I first saw the trailer without reading the summary on the {L} Pok'emon saving the world I assumed it was the sky form of Shaymin next to Pikachu.
Maybe it still is and it and Pikachu being the {L} type together bring peace..... and fields of flowers back to the destroyed landscape.
Or if it is some kind of next generation preview my money is on a sky form of Pikachu; defiantly would explain {L} part and why its ears look like multiples of Pikachu's.