My next course pretty much fills up my upload limit until I can upload up to 30 courses...
5-4: Labyrinth Castle
F256-0000-005D-B6EA
Super Mario World
https://miiverse.nintendo.net/posts/AYMHAAACAAADVHkdrOIpRw
As the name suggests, you have to go through a labyrinth of different passages. There are coins placed around different routes, and you have to pay attention to the sound effects that are played to ensure that you're heading in the right direction. The labyrinth itself isn't ridiculously long, due to the block usage limit, along with the timer. Also, with the exception of a single Buzzy Beetle, there are no enemies inside the labyrinth.
After you've completed the labyrinth, you'll then head to the sub-area, where Bowser Jr. will pursue you while riding Lakitu's Cloud. You'll have to avoid all the enemy attacks and Bowser Jr.'s fireballs as you head closer to the next pipe. Eventually, you'll see a Buzzy Beetle that you'll have to use to knock Bowser Jr. off Lakitu's Cloud. After that, finish off Bowser Jr. like normal, and then head to the next pipe.
Next up will be a battle against Bowser, but he'll be riding in a Koopa Clown Car, and the axe is blocked off by a wall that Mario can't get past without the Koopa Clown Car. As such, Mario has to hijack Bowser's Koopa Clown Car by throwing Bowser's Bob-ombs back at him. Bowser is normal-sized, so he'll fall after taking 20 Bob-omb hits. Keep in mind, however, that being able to finish the labyrinth and the Bowser Jr. phases quickly is vital if you want to have enough time to defeat Bowser; you're given the maximum 500 seconds to clear the course.