Mickey's Not So Scary Halloween Party is what you're talking about. However, I just looked at the schedule for the 21st & 22nd and it's not scheduled to happen on those days.
I posted a question about it last week since we will be there the 2nd weekend they have it planned. I wanted to know if it was worth it for the extra money you have to spend to take part.
It is taking place on the 20th and 23rd, but not sure if your schedule allows to change it so you can particpate.