Shortly after the defeat of Tirek, Princess Celestia began conducting a series of controlled and discreet experiments with a diverse family of potion types, one that allowed their alicorn users to safely witness and analyze events of the past. On the eve of the last of these such trials, a particularly potent potion among the others transports the Princess to a mysterious event far earlier in time than she had originally intended. 50,000 years earlier, in fact.
Now she's in the presence of a group of funny-looking hornless minotaurs wearing business suits.