Funny that Alicia posted that today, as I wrote this a few days ago and was debating whether to post.
Now my information is over a year old so many things may have changed from what Alicia is seeing. I am posting as a spoiler as I get a bit into the weeds. That said, this should give you a detaled idea of where they’re going with the Mario Kart attraction… changes or not.
AR = Augmented Reality
From the load area your vehicle turns right and into the large dark chamber of Bowser's castle complete with large stone sculptures of Bowser on both sides of the dual track. Ahead and also in a kart on the track is Larry Koopa playing what appears to be a lead car while Iggy is in a kart right beside you. Above and floating on his cloud is Lakitu. Straight ahead is another large standing sculpture of Bowser (maybe robotic) pointing the direction for you to drive. Larry speeds off around the corner. Your kart takes off behind but Iggy takes the lead turning right through an arch or mechanical opening doors...
Scene 2: Into the castle underground you travel with warp pipes sticking out from every direction. Various AR icons float above the track goomba, piranha, green shell are present. Here Larry spins off the track and Iggy Koop continues speeding ahead yet is quickly knocked off the track by an AR green shell.
Scene 3: Under the sea you go to Dolphin Shoals... colored warp pipes blow bubbles at you and various corals and sponges line the way. A dolphin AA does front flips and varios fish and mantas move about... some mechanical and some AR. Wendy Koopa drives onto the track out in front from a warp pipe while a shark or dolphin swims close over your head. AR points are obtained by hitting ghostly white jelly squids that line the track. Huge warp tunnel ahead!
Scene 4: Questionmark AR cubes rotate above the track as you enter this scene following Wendy in her kart. We are on Chain Chomp highway; huge chomps threaten to knock your kart off course. A giant Thwomp looms overhead a slams down on the track sending Wendy off track and then lifting in time for your kart to continue onward. The scenery is that of a country track with a bright cloudy blue sky. Lots of green hedge row trees and IP billboards and you pass a tall post mounted with cartoonish themed loud speakers. As you encounter more VR points icons, the highways starts going up hill and into the mouth of a massive barrel tunnel.
Scene 5: You exit the barrel into a raging and very cloudy lightning storm VR bolts dashing down on both sides of the highway. It all goes as quickly as it came and...
Scene 6: onto the Rainbow Road high up above and overlooking the previous track below... pillow stars float overhead and mechanical gliders fly by... The glowing rainbow road continues until you encounter various colored AR musical notes floating just above the track... as you drive through the notes a tune is played. After the last note you are now zooming downhill toward a dark forbodding scene ahead.
Scene 7: You drive right back to the depths of Bowser's Castle. Now Mario zips out in front of your kart from another warp pipe. Glowing lava glows from the walls on your left while a deep firey pit glows fire on your right. Ahead, a giant spiked ball swings in and out of the course with Iggy Koopa splattered on one side as Mario drives his kart out of sight. Fireballs and other obstacles (both mechanical and AR) threaten at every turn. And then...
MEGABOWSER and AR missles being shot at your kart
How will you ever continue?
Finally the finish line with a score board showing your points while dozens of Toads cheer you from the stands on both sides of the track.