A Rupee from The Legend of Zelda: A Link to the Past
A Rupee is a gemstone in The Legend of Zelda series that serves as a form of currency. They can usually be obtained by defeating enemies, searching through bushes or tall grass, or opening Chests. Depending on the game, Rupees have a certain amount based on the color.
Mario Kart 8/Mario Kart 8 Deluxe[]
Link just passed up a Rupee...
In Mario Kart 8, Rupees are exclusive to the first DLC pack course, Hyrule Circuit. They replace Coins, because it is, in fact, a Legend of Zelda track. Although there are many different kinds of Rupees in The Legend of Zelda, Hyrule Circuit only has Green Rupees (the lowest in value), with each of them being worth a regular Coin.
Rupees also replace the Coin Item procured from Item Boxes. You get two of them, and they give a very small boost of speed.