Sprite

Sprites are gentle forest creatures who make their only explicit appearance in Wario's Woods.

Wario's Woods
In the storyline, they lived comfortably in the Peaceful Woods, but become in danger of losing their home when Wario takes it over, renaming it "Wario's Woods" and populating it with monsters. During gameplay, a Sprite plays a key role by helping Toad clear out monsters by providing him with bombs. However, if the player doesn't keep the gauge full, she will be replaced with a Pidgit, which is also symbolized when Wario replaces Birdo on the sidelines. The Pidgit will simply shower down more monsters while Wario attempts to knock the Thwomp down, but the Sprite returns once the gauge refills, making Wario leave and Birdo come back. Two of them are also seen in the VS Mode and act identically, except Birdo and Wario do not appear. Presumably, their lives return to normal after the events of the game.

Trivia

 * The species of Wanda, the fairy character from Mario & Wario, shares the same generic name in Japanese, although she hails from a different forest and is said to be more elusive. She is also referred to as a "sprite" in English pre-release materials.
 * Additionally, the later Sprixies of Super Mario 3D World use the same generic Japanese term.