Aside from the improved quality of the Retro Courses, there are other things added to the courses like in Mario Kart 8. Some will now have paraglide, underwater and/or anti-gravity sections.
Toad's Factory (Wii)
A paraglide section has been added at the part of the moving platforms. Not far further, after the part where the alarms go off, another paraglide section has been added as you jump out of the alarm zone. When you reach the buildozers you can drive in anti-gravity on the sides of the bulldozers and you end with an optional paraglide if you don't go into anti-gravity.
Boo Lake (GBA)
Boo Lake got a big make-over. The first bridge has been replaced to make it a real shortcut, and the second bridge has a shorter turn. All the gaps in the pier look like they are broken gaps in the pier, they also don't have any jumps in front of them. Boos with lanterns are floating over the stage. The many jumps near the end of the stage have been replaced with broken planks which also can be used as jumps. The mansion is now placed on the left side near the start and the creepy forest in the background is like the one in Super Mario Bros U.
When you fall off of the pier, or fall through one of the gaps you won't immediately be pulled back by Lakitu. You can drive underneath the pier in the water, which has about the same height as the one in Cheep Cheep Beach. You can drive up by using planks that lead you back on the pier again, but you're forced to go up at the giant gap in the pier near the finish.
Twisted Mansion (Wii U)
Shy Guy Bazaar (3DS)
The only change is that the alternate path in the actual bazaar (on the right side) now is an anti-gravity section on the side of the wall.
DK Summit (Wii)
The obvious change is that you open your paraglider when you enter the canon to go up the mountain. The first jump you encounter also changed into a paraglide jump. The two sharp turns after the series of small hills has turned into an anti-gravity section.
Cheese Land (GBA)
The molten cheese puddles make you spin on the place, as if it was oil. After the second turn you will enter a cheese tower, a drastic change from the previous version. You will now drive upwards in the tower. The first jump goes over the first floor and the jump on the second floor is a paraglide jump. Several Little Mousers are now only near the end of the course.
Mario Circuit (3DS)
The only change is the anti-gravity section in the pipe tunnel near the end. Nothing else.
Thwomp Ruins (Wii U)
Vanilla Lake 1 (SNES)
Everything obviously has become much bigger and wider to make it a decent race track. Just like the remake of the N64 Sherbet Land everything will be slippery. The first item boxes have move closer to the finish and right after that is a gap in the track which allows you to race on the underwater track. The blocks you had to jump over are removed and replaced with icicles. The second big gap in the track also allows you to drive underwater. However the gigantic one near the end is the one that brings you back on the surface. Another set of item boxes have been added right after the second coin pack.
Aside from the new track design the background is now filled with high snow covered mountains but it is still set in bright daylight. The rainbow colored blocks are now ice blocks covered with a layer of snow. In the background are some Mr. Blizzards. And underwater are the extend of the icicles on the surface that thus are way bigger.
Mount Wario (Wii U)
Neo Bowser City (3DS)
Not much has changed except that the bridge you drive over has transformed into a corkscrew bridge which is now in anti-gravity. It basically are two corkscrews after each other but it retains the same design as the bridge in Mario Kart 7.
Mushroom City (GCN)
Also not much has changed in this course. Like in Toad's Turnpike there are some cars that have jumps on them but no paraglide jumps. Near the end is a part where there is road on the left but a gap on the right. Now you can drive in anti-gravity one the right wall.
Wario Stadium (N64)
The changes made on the track itself are the water section in the part where there are many small hills. It is very dirty water so it is harder to see under water. There are many jumps on the track on which you now obviously can preform stunts on. Before the finish there is a bigger jump on which you jump over a gap and you can paraglide now. The part at the first U-turn has turned into an anti-gravity section as you practically drive on the side of a giant pile of dirt sand.
Bone Dry Dunes (Wii U)
Wario Colosseum (GBA)
The course is changed into a one lap round. So the who course itself has been extended. The big jump into the spiral is now a paraglide jump so the length has been extended between the jump and the landing spot. You immediately enter anti-gravity as you drive down. This goes on until the line where the Wario sign points down. Then you come at the part with the big jump. You can drive in anti-gravity on the side of the cage and paraglide jump over the gap in the middle. You can also paraglide on top of the roof of the next section and jump down from there. Of course you can also drive underneath. The last jump is also a big paraglide jump. The paraglide jumps obviously make the course a lot bigger.
Lakeside Park (GBA)
Aside from the visual upgrade not too much has changed. Like in Donut Plains 3 it doesn't matter if you drive off the bridge as you can drive underwater. You can even take a shortcut throught the water to the other side. Although there is only a small path that leads to there underwater so you have to land correctly. The big jump remains a big jump but the landing part is made bigger to make the changes smaller for you to bump against the side. The volcano fires meteors similar to the ones from Grumble Volcano and also leaves that same effect behind.
The eggs on the side of the road are now Plessie eggs. Plessie himself also can be seen swimming around in the water. Aside from Plessie several Baby Yoshi's can be spotted around the track.
Cloudtop Cruise (Wii U)
Rosalina's Ice World (3DS)
Nothing has changed except for the anti-gravity part at the very beginning until you enter the ice village.
Bowser Castle 4 (GBA)
Nothing aside from a visual upgrade and a paraglide jump near the end. There however is a big difference, the ground is designed as the last level in NSMBU and has the same background as in that game as well. Some lava sprouts have been replaced with moving Magmaws.
Rainbow Road (DS)
Nothing has changed here either. The parts like the loop and the corkscrew in which you couldn't move that much have been changed into anti-gravity parts. And the part where you fall down on a lower part of the road has been changed into a jump. The Rainbow Road is now set above the clouds and a clocktower.