Derpy shouldn't have touched that button.

Now that she has, the TARDIS's console has been compromised, and it's refusing to recharge at any kind of fast rate- quite the opposite, in fact. But when they step out of the TARDIS, they find themselves on the edge of a lake, where Ponyville should be. As they try to fix this, a war rages around them. And if wounds don't heal soon, they Equestria will be doomed.