While I ended up missing the Hallowed Helm, two Squashling pets dropped out of five tries, which was a pretty good deal for the short time we had. We ran out of time on the last summon... as my guildie completed the quest to call out the Headless Horseman, he was able to utter the challenge but nothing came out from the grave. In fact, as the clock struck precisely at 4pm, the giant pumpkin disappeared, leaving us stupefied.
It was a fun Hallow's End event, even if it did get rudely interrupted by zombies. I hope that unlike me, most of you got what you needed from the event. The mount would've been nice, but I suppose there's always next year. By that time, I hope Blizzard will update the encounter for Level 80 with matching new loot. The Headless Horseman has about 12 months to level up.