From the Super Mario Wiki
The 3-Up Moon is an item that first appeared in Super Mario World. It is a yellow, crescent-shaped moon that sports eyes and a smile. An extremely rare item, the 3-Up Moon functions very similarly to the 1-Up Mushroom, but true to its name, it instead rewards Mario or Luigi three extra lives instead of one.
Super Mario series
Super Mario World
The locations of the 3-Up Moons in Super Mario World are as follows. If the player replays the level, the moon will disappear from where it was until the game is reset. Most, but not all, 3-Up Moons are only accessible if Mario or Luigi is utilizing their caped form.
Additionally, the moon seen in Star World of Super Mario World resembles a 3-Up Moon.
Super Mario Advance 4: Super Mario Bros. 3
Game and Watch Gallery 4
Appears in the "FIRE" mingame, they come out of Yoshi eggs and give multiple points when bounced.
New Super Mario Bros. 2
New Super Mario Bros. U
3-Up Moons reappear in New Super Mario Bros. U. They are found within 3-Up Moon Blocks and a total of four 3-Up Moons can appear, though they can only be collected with the efforts of the GamePad player and Wii Remote player(s).
In Mario Family, there is a sewing design of a 3-Up Moon.
The 3-Up Moon makes an appearance in volume 3 of the Super Mario-Kun. It serves a different purpose, powering-up Mario rather than granting him 3 extra lives. This allows Mario to defeat a Buzzy Beetle-like enemy.
Names in other languages