3-Up Moons are moon-like items that only appear in Super Mario World. They are shaped like moons, have eyes, and can be found on the ground, however they are extremely rare, with only seven appearing in the entire game (one in each normal world). They have a similar effect as 1-Up Mushrooms, however they give Mario or Luigi three extra lives instead of one. Also, they can only be collected once, if the player replays the level, the moon will disappear from where it was. 3-Up Moons also appear in New Super Mario Bros. U and New Super Luigi U.
In Mario Family, interestingly; there is a sewing design of this item in the game.
In Japan, players could scan the Blue Switch e-Reader card, and obtain 3-Up Moons in Super Mario Advance 4: Super Mario Bros. 3.