MK does a big thing with singing and dancing and Mickey arriving on the train. Steamers are shot out. It is fun.
Epcot used to bring the characters out in a big bus. I don't know if they're still doing it.
MGM does a thing with a family chosen to be actors and they help open the park. I don't pay it much attention.
AK has the Minnie and Goofy and someone else, I think, come out on a van and go over safety stuff. They talk about some other stuff, make sure they have their cameras and park maps. Mickey makes an appearance off in the distance.
