'Tis the season, Debra!
It's a pleasure to welcome you back to planDisney, and we appreciate you reaching out with your question. You're going to be visiting Walt Disney World during the most MERRIEST time of the year...how exciting! The 
holiday season at Disney is pure magic. And since you're attending 
Mickey's Very Merry Christmas Party, you'll get to experience the ultimate dose of holiday joy. From snowfall on Main Street, U.S.A., to those delicious complimentary cookies and hot cocoa. You're in for a holly jolly good time!
Lightning Lane Multi Pass is such a fantastic way to maximize your time during busy park days, helping you experience more of your must-do attractions with less waiting. However, it isn't available for use during Mickey's Very Merry Christmas Party. While that might sound like a Bibbidi Bobbidi bummer, there's plenty of good news ahead! Attraction wait times during the party are typically much shorter, meaning you can often hop right on to your favorites without much of a wait at all.
Here's what I'd suggest: since you have a Park Hopper ticket, spend the daytime hours checking off your must-do attractions while the Lightning Lane is available to use. That way, you can experience all of your favorite rides before the holiday festivities begin. Then, once the party officially kicks off at 7:00 PM, let the merry magic take over!
Debra, I hope this information has been helpful as you continue to plan your very merry holiday! I'm wishing you the best time ever! If you have any other questions, you're always welcome back here at planDisney!
Merry Wishes,
Kami