Hi Loretta!
Mickey's Not So Scary Halloween Party is a big favorite in our house! We love the special Halloween parade and being able to trick-or-treat inside of Magic Kingdom:)
The party does require a special admission ticket. A park hopper or regular ticket will not work. They clear the park of all guests without party tickets at 7 p.m. Cast Members will be standing throughout the park checking for party tickets. You will get a wristband to identify that you have a party ticket.
You can purchase
party tickets on the Disney World website. They will be mailed to you.
Tip: They usually let party ticket holders into the park starting around 4 p.m., even though the party isn't officially until 7 p.m. If you have used your park hopper that day anyway, it won't matter, but if you wanted to save a day that would give you three extra hours. Sometimes, we use that day as a resort/swim day, then head to the parks at 4. Be sure and ask a cast member during your stay if they will be doing that as it is always subject to change.
I hope this helps! Please let me know if you have any other questions.