This story is a sequel to A Griffon's Fate

The griffons are attacking Los Pegasus, and Celestia has sent her guard to protect the city. Everypony thinks that the royal guard will be victorious, but when a lone pegasus returns to Canterlot and reports that the guard ponies have been wiped out, Princess Celestia quickly orders a search and rescue effort be made. By the time the first rescue team arrives the city has been abandoned and dead bodies of ponies and griffons litter the streets.

During the recovery effort, one pony finds a corpse clutching a book to his chest. It turns out that this book is the dead pony's diary, and it is the only written account of what happened during the battle. This is that story;