Homura may be able to stop time for a short period of time these days, but it's enough to determined the creature's appearance; A Shadow Moth. This creature takes the shadows of people to become bigger and faster. Now that Homura has managed to see it, it will turn into a giant mothman and attack them with shadow-y vines!

If hit by the vines, characters would start doing everything backwards. That would explain the grandfather clock going backwards, we suppose! Either way, the Moth's goal is to eat them for even more energy, but it's not too difficult to defeat. It's just very, very fast.