Recreating spells that are long forgotten is risky, really risky, but Twilight's finally mastered the spell. Excited about her accomplishment, she goes to demonstrate to her friends of said spell. However, she makes an error when Pinkie Pie won't sit still enough and accidentally causes Twilight to make an error.
And now there's a wolf-pony-like-thing, who seems dead set on smoking.

It's one thing to be interrupted when solving a murder case, it's a completely new level of annoyance when you're sucked completely out of your world, but it's a real big problem on your hands when you're right back where you started before Fabletown.
An animal.

And All Bigby wants to do is go back to Fabletown, but until Twilight can revert her spell, Bigby's gotta bite the silver bullet on this one.