We got the 50 coins! That was too easy, but it was fun playing through some MKDS to find her. I thought she might appear on a Yoshi-themed track. 
Okay, I see that. I'm going to submit that answer, since we do have 3 guesses. He matches every description. Great job Sir Mario!Sir Mario said:I believe it's Fyrus, a boss in Zelda Twilight Princess.
He's deep in the Goron Mines, he's huge and is broke free from his chains so you don't hear a chain rattling.