I think it is way too hard. I tried already, I was only on the Krokosphinx at the time, so I had to get a friend to get me into Chelsea Court. I had a fire elemental minion and I still couldn't beat Nimah! She has 5,000 health and a 1,750 health minion. I didn't even beat the minion! Please make this easier KI.
I'm also hoping the Fire minion quest is eaiser than the Ice minion quest!
Sorry to hear about your issues with fighting the boss for your minion quest. I can give you some tips if you give me your secondary school(s) and deck construction.
But on the bright side, the fire minion quest is extremely easy, so your pyromancer should have no problem!