This story takes place mid-season two.

Cannon Feather is a new royal guard doing his best to keep the castle safe, but one evening, he and all of his brothers and sisters on duty suddenly, without warning, regressed into foals. It doesn't take long for the princesses to discover this and put a plan in action to find out what caused them to regress and find a cure. The Princesses learn it's an ancient disease called "phoenix flu," and they now have to quarantine the castle to keep it from spreading and care for the foals as they administer the cure. Meanwhile, Cannon Feather and his fellow royal guards get up to some fun shenanigans to keep the princesses busy.