This story is a sequel to Doctor Whooves: When Universes Collide
The holidays at Canterlot High are always lovely. Bells ring, children sing, and old friends reunite. Sunset and her friends are in good cheers when the Doctor returns for a visit. However, he discovers a crack in time leading to Equestria. Even when he closes it, the crack returns, and a swarm if Changelings comes out of it. With the TARDIS sent off who knows where, the Doctor is stuck between a rock and a hard place, as he must protect all of Canterlot High's students from the Changeling Invasion.
'Alternate Universe' tag for slight differences in the timeline.