I just tested my above fire/entropy deck in the trainer against Ferox and it absolutely dominated him, even with numerous play mistakes on my part. Few small pieces of advice when playing him, though they aren't crucial they do help ensure the win:
1. Don't antimatter more than one dragon unless you have to - it doubles his healing.
2. Don't play a Fire Spirit until you have your Shield up.
3. Don't neglect to boost your spirits or play any extra demons once you have the field under control.
4. If Ferox gets TWO dragons out before you have a Demon up, try to use Antimatter first instead. I lost my second try against him by making this mistake.
I do seem to have a ton of extra Entropy quanta floating around. But overall, I think this deck is almost a sure win against Ferox. I may use it myself outside the trainer when I know he's coming.
EDIT: Changed the mark to Fire and dropped one Burning Pillar and one Demon in favor of two more Amethyst Pillars. Played several games against other gods just to see what the average draw looked like, and in general I had trouble getting Fire Shields out early enough, while I always had excess Entropy and several pillars out.
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Results:
Game 1 - Total deck wreckage. He never stood a chance, I got established fast.
Game 2 - Loss due to playing a Demon instead of Antimatter when he got two dragons out early.
Game 3 - Win, but ONE turn from deckout due to Antimattering two dragons. Could maybe have lived without doing so.
Game 4 - Loss due to playing a FIRE SPIRIT when I needed to be saving up for a Fire Shield! I am an idiot. It was totally possible.
Game 5 - Loss due to more mistakes - mainly waiting on Antimatter when I should have had a Demon out earlier.
Game 6 - Zero mistakes, super easy victory.
Game 7 - Scary victory, he didn't get any dragons out until late and the Frogs/Cockatrices kept coming, so I was forced to Antimatter a Frog. Then he plopped out a dragon and got me to 3 health. Lucky recovery.
Game 8 - Another win one turn from deckout, thanks to two Fire Spirits being at the very bottom of my deck.
Game 9 - Was in critical danger of deckout so I re-anti'd his dragon and killed it, but he took me out as a result. Super fast setup does NOT help when I don't draw a Fire Spirit until my deck's down to 8... horrible draw. I'm dropping an Amethyst Pillar for another Fire Spirit.
Game 10 - He got a blitz start and outpaced 17 Antimatter-healing... ouch. All Demons were bottom half of my deck. Guess what I drew two of at the start?
It's becoming clear that 1) if you don't make mistakes, you need an awful draw to lose, and 2) this deck upped would be insane against Ferox. It's brutal enough as is. Fire mark was absolutely the way to go here, as fire shield is vital.