So, i came up a dumb idea to represent slimermin the maze. Get a blackout actor [actor covered in black], and paint on the chest and arms a realistic looking slimer, then position the actor against a black wall, boom now you have a slimer floating and running towards you.
This is how they did a couple scares in Poltergeist last year with the floating skulls. My worry is how Slimer would look and move in this way alone. I could see it being a puppet or animatronic or a combination of costume and puppet/animatronic.
I like the idea of using some 3D effects to make it appear that he, or other characters, are moving through the walls to set up a scare in another room. At this point I am so excited to have a GB house that I think I will actually cry if it doesn't end up coming this year.