We ended our campaign with a gigantic battle, and Boston in smoking ruins.
First an NPC Warden, who was the girlfriend of one of the characters, killed herself with a deathcurse, where she drew upon all the power of the the Walker that had possessed her. That vaporized a huge area near Chicago with a diameter of many miles, it burned with an purple flame that didn't even leave ashes behind. And even things like steel and concrete burned. All electronics in a 30-mile radius from the blast was destroyed.
And then came the events in Boston: Turned out that a bunch of dwarves that had been living in a below-gorund comlex undeer the house of one of characters, had dug too deep, and had been to greedy. The city had first been hit by a couple of major Earthquakes and a huge sinkhole had appeared right where said house had been. And from that sinkhole cama a huge fiery being (a balrog, or one of the characters who was a svartalf said it was Surtr, the fire-giant who would destroy the world), and it was followed by an army of goblins and svartalves.
The national guard came. Lots of wardens of the White council came, along with an army of Winter trolls that we were on firendly terms with due to their king being the adoptetd son of one of the characters. We had 3 old faeire queens wo where now vassals of said troll king, Harry Dresden arrived, Vadderung came with a host of Valkyries and Einhärjars, One of the characters who was a changeling summer prince (he had just gotten promoted to duke and been turned a full shidhe came with his retinue)... My character's girlfriend who was an extremely powerful (reformed) necromancer animated the fallen soldiers so they could keep fighting. I did what I could with divinations to act as a living comm-center and give information to my master who was there and helped the wardens.
In the end, it was our Genie who decided to take a huge fire-form and battle the balrog with her magical sword. We all pooled out recources to help out. I gave it all to find some weakness that the Genie could use, the summer prince used his magic, as did the wizard whose girlfriend had sacrificed herself erlier to destroy the walker. So we beat the Balrog, and then the others could deal with the rest of the army.
/Ulfgeir