They could also go for that Adren/Elf deck they used a round or so back, by the way. Also, don't test decks, at least with your main accounts. As we are learning, other teams are spectating matches between War members, which is, undoubtedly, how some perfect counters were made.
Anyway, it's freaking Entropy, they are going to counter whatever we play, no doubt. We should just play the stronger of our two primary decks (Fractal Mummies or Flying Arsenics) and hope for the best. Adding more cards for a deckout may seem like a good thought, but that is also what ruined icb's deck two rounds ago, where he lost by not drawing the cards he needed.
Let's just pick one and stick with it. I'm fine with 31 cards, but any higher than that and we are reducing our chances of winning. In either deck we use, they will likely bring Purify, worst-case-scenario, so let's just poison them some more. Flying Arsenics are actually a counter to Antimatter and, mostly, Pandemonium, which are the two cards we should worry about most.