How on Earth do they do that?
I guess its OK to say how the mirror effect is done:
There are several moving "walls".
1. On the "right" of the mirror is a wall which moves to the right, it "overlapps" the top the mirror frame at the frame level, but the wall part is flush with the non-moving wall.
2. On the "left" of the mirror is a wall which moves to the left, it "overlapps" the top the mirror frame.
3. Similarly, the bottom of the mirror has a "bottom wall" which moves down as it overlaps the "mirror" which is really a door with LED screens hidden behind of these two-way mirrors.
4. The mirror is a real mirror in that it is made of 2 two-way mirrors, which appears as a normal mirror in normal light, but when they turn down the lights the LED screens behind it lit up and change to reveal the castle and then a door pattern and it opens up as a "door", where you can walk into the room behind it.
5. Projections are digitally mapped to the mirror/door frame and projected on to it while it moves to create the magic sparkles.
6. Note that the "top" of the mirror does not move up.
The castmember has to ask everybody to "stand back" as little fingers could theoretically get caught in the moving walls, especially when it closes back-up.