Please sticky, or upvote this so everyone sees it. :)
Guide to "Let the Fires Come!" and "Stop the Fires!"
First off let me explain how doing this on multiple characters works. There are so many people that have no idea how to do this on alts, and how to not mess it up for people with alts that its frustrating for them to do it.
So how this event works, is there is a quest "Let the Fires Come!" that starts the event, once the event starts, it changes to "Stop the Fires!". The quest you want on your alts, is "Stop the Fires!", now here is why. Pick up the quest "Stop the Fires!" on everyone of your alts. Go back to your first character, and wait for the event to end, either with killing the Shade, or failing. Now pick up "Let the Fires Come!" This starts the event. Complete the event, and turn in. Login to your next alt, run out of the brill inn, and "Stop the Fires!" quest will complete, use the head to get the other quest from that, turn them both in. Run back to inn, login to your next character, rinse and repeat, until the event is over. IF YOU HAVE THE QUEST "Let the Fires Come" it WILL NOT COMPLETE ON YOUR ALTS!
THE PROBLEM WITH NOT KNOWING THIS!
So say you log onto an alt, and the pumpkin head is there, but the "Stop the Fires!" quest isn't completing... Strange right? Well its not, essentially what happened was someone went and started the event, which means the "event clearing" is gone, so that quest can no longer be handed in, until its done again. So please, for everyone's sanity, IF THE PUMPKIN HEAD IS ON THE GROUND, DO NOT PICKUP THE QUEST "Let the Fires Come!", it will clear the completion of the event, and essentially mess it up for people doing it on multiple characters.
SIDE NOTE!
If you don't see any fires left, and it hasn't completed, there is a little tent with supplies under it, with a jack o' lantern ontop of the tent. Under that Lantern is a fire that typically no one saw to put out. Also, Work on the same building, right to left, it'll actually complete if you do because the fires spread so quickly now.