All Bobs Must Die:

They thought it was relatively safe. The twins were being sent out with a group of people that were essentially adults. Even Raph was an older teen and probably more experienced at fighting than all of them put together. The fearling they were looking for wasn't even that powerful, if the mini-fairies were to be believed. It was a construct, several fearlings reconfigured into something new, but not that powerful.

It needed to be hunted down and destroyed but it was something that Mabel alone could've handled. Between the five of them, they made short work of it and it looked to be a nice little on-the-job lesson for the twins, where they got to fight while under the protection and guidance of the others.

The problem was the fear. Fear was always the problem. That fear was just a coincidence but as coincidences sometimes went, it was a dangerous coincidence.

Not far from where they'd destroyed the fearling, there was a little girl who had played one of her older sister's video games and it had frightened her. As she went to bed that night with the fear clutching at her heart, the only thought that helped her fight the fear was the thought of two of her favorite cartoon characters - ones that fought scary things like ghosts all the time - fighting the scary ghosts in the game.

She knew they were the kind of twins that could beat the ghosts. That was the thought she fell asleep to, a thought that gained power in that twilight between waking and sleeping.

Where they were in the woods, that thought - and that fear - temporarily took on a life of its own, reshaping reality and assigning them all roles in the story it was trying to mold. A sudden mist swept through the dark woods and every myth in the group found themselves powerless. They still had their gear and their skill and wit but their myth powers were gone.

Even worse than that, as the mist obscured them from each other and they suddenly found themselves separated. They were suddenly all in different sections of an ancient, decrepit Japanese village, one that was caught in a strange and eerie twilight. Dancing around them in the breeze were glowing crimson butterflies that fluttered off, as if they were showing them which way they should go.

Whether it was safe to follow them or not was the question at hand.