Mist Form - boss location

I really need to acquire the ability "Mist Form" for my elementalist. I know that a couple of bosses have the ability, and the closest one to me is "Frash the Cold" since I'm at the Temple of Ages.

Can someone please help me find this boss? I can only find the lvl 28 necro boss (death shadow or something like that)

Thanx a lot

You'll find Mist form in the Iron mines mission, on the boss you have to kill to get infused.