Submarine

A submarine is a type of underwater vehicle, used in both the Mushroom Kingdom and the real world.

Super Mario Land
In the Muda Kingdom area, Mario can use his submarine, the Marine Pop.

New Super Mario Bros. U
Although a real submarine doesn't appear in New Super Mario Bros. U, the course, The Mighty Cannonship's boss uses Bowser Jr. using his Koopa Clown Car for an underwater battle, adding a air tank, which gives it a submarine style machine.

New Super Luigi U
The Koopa Clown Car's air tank is used again in All Aboard!, with Bowser Jr. as the boss again in New Super Luigi U.

Mario Kart 8
Submarines are seen in Mario Kart 8. They appear in the course Water Park, where they are controlled by Nokis. Also a stamp can be unlocked in the game.

Trivia

 * Super Mario Land & Mario Kart 8 are the only games featuring real submarines.