What is so fragile it already breaks when you just say it's name?

Three words, seven letters Say it, and the key will be revealed.

With spikes on my shell and fire in my breath, I challenge a hero at risk of his death. A villain, a king, the foe you all know, Guess who I am, come on, have a go!

Always in your sight, but rarely truly seen. A rest for glass, holding treasure green. What am I? The answer is right in front of you.

I contain many letters, countless in fact, yet my name consists of only two words, for a total of ten letters. What am I?