Made by Christian “Cynical” Diaz, the purpose of these transitions was to eliminate the black screen when loading the map in Mario Kart Wii for the audience to have a fluid transition to.
Regular Tracks are what Nintendo made to be intended in the Vanilla version of Mario Kart Wii.
Custom Tracks are what CTGP, the most standard mod pack for competitive play, allows to be in their mod pack managed by 🇬🇧 Robert “MrBean35000vr” Chadwick and his brother 🇬🇧 Alex “Chadderz” Chadwick*. A bit of history, these two were the first to crack the security code of the Wii in 2009, which led them to have the biggest influence on Custom Tracks in the community.*
The tools/programs used to make all of these are the following:
NoClip with its Guide/Command List
Here are the regular track transitions: Regular Tracks Track Transitions
Here are the custom track transitions: