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Kotaku ran a really cool article on Mario and Zelda crossovers. Check out the full story here.
The very first Mario reference in the Zelda series can be found in the very first game—Manhandla, the third boss of The Legend of Zelda, is described by the Japanese (and only the Japanese) manual as a four-limbed, massive Piranha Plant.
A Mario reference pops up very early in the game, with portraits of Mario hanging on the walls of some of the houses in Kakariko village. Furthermore, Chain Chomps appear as enemies in one of the dungeons, and there are also traps called Guruguru Bars strewn throughout the game which greatly resemble Mario’s Fire Bars.
In Majora’s Mask, the Happy Mask Salesman has several masks on his backpack—one of them being, as you can see, a Mario mask. Also, there are Mario bros. lookalikes in this game as well:Mr. Barten, the owner of the Milk Bar, looks like Mario, while each of the three Gorman brothers resemble Luigi.
