Fountain of Youth

The Fountain of Youth is a magical fountain that appears in The Super Mario Bros. Super Show! episode "Two Plumbers and a Baby". It is located in the Kingdom of Youth. The Fountain of Youth can make any person any age they want, which is due to a lever which regulates the amount of rejuvenating water deposited into the fountain.

In the episode, three elderly people try to become eighteen again; however King Goo Goo Ga Ga Koopa pulls the lever to the maximum setting, which causes the old men become babies instead. Princess Toadstool then falls into the Fountain of Youth and is turned into a baby version of herself. Later, when attempting to turn Mario, Luigi, and Toad into babies, King Goo Goo Ga Ga Koopa falls into the Fountain of Youth and becomes a baby himself.

Mario and Luigi later reverse the flow of the Fountain of Youth, and revert Princess Toadstool to a full-grown woman. They also free Koopa's baby captives by returning them to their proper age. The old people thank Luigi and Mario and express gladness to be adults again.