Hi, Shelbi! Thanks for visiting the Disney Parks Moms Panel and asking your question!
The dress you describe sounds so cool! Themed dresses are totally acceptable at the parks and I see lots of really neat designs each time I visit. As long as it doesn't look like an actual Ursula costume, isn't too layered, and doesn't drag on the ground, you should be good to go.
You might also want to check out the many beautiful vintage-inspired Disney dresses in the
Disney Dress Shop in the Downtown Disney District and Le Bat en Rouge in New Orleans Square. There are so many adorable dresses featuring characters and attractions from the theme parks. They also sell perfectly matching accessories like purses shaped like carousel horses and dole whips, to name a few.
If you are attending
Mickey's Halloween Party during your visit, then adults are welcome to dress in
costumes for the party. While you still can't wear anything that drags on the ground or covers your face, you can most certainly let your creativity shine if you have tickets to this special event.
I hope this helps. Have a spooktacular time at the Happiest Place on Earth!
-Linda