Just before release of the original PC version of Volgarr the Viking, Worlds 2 & 3 were swapped.
Originally, the Undead-themed world was supposed to be World 2, and the Water-themed world was supposed to be World 3. I therefore intended to make the Water-themed world more difficult than the Undead-themed world when designing them. I even chose the order partially based on palettes with the idea of swapping back and forth between brighter and darker color schemes for an almost day-night cycle feel - Jungle would use brighter daytime colors, Undead dark/night, Water bright, Fire dark, Sky bright, Tower dark...
However, being the developer sometimes it is hard to judge the difficulty of your own game since you are so intimately familiar with it, so I asked beta testers what they thought of the relative difficulty of each World. The voting came out that the Undead world was more difficult than the Water world, and so I swapped them for release.
After release though, and seeing how much people struggled with the Water-themed World, I felt that perhaps the beta testers were a bit biased in their feedback and that my original intended order would have made for a smoother difficulty curve.
You see, for the testers, the first level they ever got to play was the Undead-themed world (its a good practice in game design to design a "middle" level first, and do the first and last levels near the end of development, for reasons I won't delve into here). So, to them, the Undead world probably seemed super difficult as they had never played the game before when they got to try it. By contrast, the Water-themed world was one of the last levels created (due to the extra work for water physics) and thus by the time the testers got to play it, they were already very familiar with the game, having been testing it for months by that point, and didn't struggle with it much. I'm sure some of the testers reading this probably still think I'm wrong but after watching so many playthroughs of our game, I'm convinced the Water world is more difficult to a new player than the Undead world would be.
Regardless, once the game was out I couldn't swap the levels because of Leaderboards getting messed up by the change. When I realized that Wii U and Switch didn't have any built-in Leaderboard support, I saw an opportunity to finally put the levels back in the order I originally intended them to be, since there would be no issue with the Leaderboards not matching other platforms. I also feel like in some ways Nintendo fans are kind of in their own unique gaming ecosystem and so having the Nintendo version be different than all other platforms wouldn't (hopefully) bother them much, especially as I suspect many of them will not have played the game on another platform before anyway.