Disaster strikes! Multiple times!

Or perhaps not at all, depending on how real unreal things are. MLP has a weird philosophy regarding time travel.

( spoilers )

I'll give it 3/3 even if the ending wasn't exactly what I would have wanted. The solution was logical in broad stokes, and it was only some of the details that fell flat. Meanwhile, the rest of the episode was an excuse to wow us with stuff, and it did.