Since legendary game-developer Shigeru Miyamoto created both the Mario and the Zelda series, Nintendo's favorite plumber and his friends make quite a few appearances in the Zelda series. Like a Mario painting in a house in A Link to the Past.
But not just Mario appears, but the Chain-Chomps as well. An interesting thing to note is that they were intended to be in the Zelda games first, but ended up having their initial appearance in Super Mario Bros. 3 in 1988.
They also made an appearance in Link's Awakening, as Bowwow who symbolized a dog. The reason for this is that the Chain-Chomps were inspired by a dog that scared Shigeru Miyamoto as a child.
Link's Awakening has a lot of Mario cameos to say the least. Luigi got demoted to raising chickens.
Some girl think she looks like Princess Peach.
And you can win a Yoshi doll in a mini-game. I loved this one.
Wart also made an appearance with his original Japanese name Mamu. Instead of being an evil boss like in Mario, he's a good ally who teaches Link a song.
In Ocarina of Time, you can notice that Hyrule Castle loves Super Mario 64.
And that the Happy Mask Salesman in Majora's Mask is also a Mario fan. I can't blame him.