Hi Laura,
October might very well be my favorite month to visit Walt Disney World. One of the reasons is that I absolutely love
Mickey's Not So Scary Halloween Party. I look forward to it every year!
You asked a great question about the tickets. You are correct in that entry to Mickey's Not So Scary Halloween Party requires separate admission. However, if you plan to spend the entire day at the Magic Kingdom, then you will need regular park admission when you enter earlier that day.
On any given day when a Mickey's Not So Scary Halloween Party is being held, guests are reminded that the Magic Kingdom will be closing early (usually at 7:00 PM). Guests that have tickets for that evening's event will be asked to exit the theme park and then re-enter with their tickets for Mickey's Not So Scary Halloween Party. Upon re-entering the Magic Kingdom, guests will receive a special bracelet so the cast members can easily tell which guests have valid admission.
Here's a little tip from your buddy Derek:
While there are so many special surprises in store during Mickey's Not So Scary Halloween Party, make sure you plan to catch the fireworks presentation - Happy HalloWishes. I don't want to spoil it, but I will say that the finale is amazing! Your best spot to view this show would probably be someplace where you can get a clear view of the front of Cinderella's Castle.
I hope that helps! If you should have any additional questions, please feel free to write back and I'll be happy to help in any way that I can.
Best regards,
Derek