From the Super Mario Wiki
The Triplets are three Goombette siblings from Super Mario RPG: Legend of the Seven Stars. They are the nephews of a Goomba named simply "Goomba" and run their own small shop out of Goomba's shop in Monstro Town. The only item they sell is a variety of Mushroom that turns the party member it is used on into a Mushroom (like the effect of the Funguspike or Petal Blast attacks). The item restores 30 HP immediately, and the party member, though unable to attack, continues to steadily recover more HP until the effect wears off as usual.