Murder On Equestrian Island

Thirteen ponies are invited to the new Equestrian Island off the coast of Gallipoli. The first day passes without incident but by the night of the second, one of them is dead. They are stranded there for the duration of the visit, with a crime so well-premeditated even the pegasi and unicorns are helpless to escape. Killed off one-by-one along the lines of an ancient nursery rhyme, who will be the next to die and will any of them survive?

Author's Note:
Inspired by Agatha Christie's And There Were None.
This story takes place before the beginning of Friendship Is Magic. The Mane 6 have (mostly) never met.