Hi there, Alexandra, and welcome to planDisney! I am so glad you found us to ask your questions about special events at Disneyland.
When you purchase a ticket for a special event, such as Oogie Boogie Bash or Disney Merriest Nights, that ticket is your admission into both the theme park and the party. You will be allowed to enter the park at a certain time, 3pm for
Oogie Boogie Bash, 5pm for Merriest Nights. If you would like to spend the day at either of the theme parks before this time, you would need a separate admission ticket.
Looks like you are planning to attend
Disney Merriest Nights! I can’t wait to see Sleeping Beauty Castle all draped in icicles, and Haunted Mansion holiday is one of the best things ever!
I hope this clears up any confusion for you.
Happy Visiting,
Tracy