Upon creating a save file on the file selection screen, the player will be prompted to choose a difficulty. There are 3 options: Normal, Hard, and Ultra-Spicy, in increasing order of difficulty. The latter can only be unlocked once the player has completed the story mode in Hard difficulty, or completed the demo.
At any point in the saved game selection screen, the player can press to change a file's difficulty, but doing so makes it impossible for the player to earn any badge related to completing Story Mode in a given difficulty, in that file. If the player uses this option to change to the exact same difficulty the file is already at, nothing will happen.
The following is a list of known differences between difficulty modes. The Wii U version of Pikmin 3 is included for comparison's sake.
In addition, in Normal difficulty, having the active leader collect a data file will automatically open it, whereas in the other difficulties, this is only true for some data files.
In other game modes
Internally, other game modes use rules based off of specific difficulty modes. Each stage is capable of specifying what difficulty mode it uses.