"To obtain, something of equal value must be lost. This is Alchemy's first law of equivalent exchange."
"Pony transmutation is the ultimate taboo. This is Alchemy's second law."

Princess Twilight Sparkle didn't realize that this was going to apply to more than just the unique type of magic she discovers in the vaults of Canterlot Castle. Though alchemy gives her powers she never thought possible, she doesn't realize the cost of such an exchange until it is far too late. This is what happens when it all goes wrong.