I mean, whatever, dress up days when I used to work retail were a bit of fun that broke up the monotony for the lifers. I hated it then as well but at least it was optional.
Having an employee dress up day/event and then making staff pay for it if they opt in is gross and dumb.
You got into a marketing arrangement with Disney, that both of you profit from, you fucking pay for it. Greedy mfers honestly expect staff to fund their cross promotion with a $155bn company.