The thing is, that since they're in such a difficult situation, I can guarantee that they will test every one of their decks against Bonebolt because it is quite possibly the most powerful deck we have at our disposal. Now if Fire does their testing right then they will realize that Arsenic actually provides us with a win possibility against FSS, which makes Deflag a very worthy addition in this case. Lord knows they have the deck space to use it if they wanted to. But yes, Arsenic is very fail against their other decks, and based on the RNG necessity of their Immobow, I'm not sure I would want to risk adding another Arsenic and reducing our chances of drawing something much more important.
I've wondered whether Ivory Dragons would be a good addition here, but I've about convinced myself they wouldn't change the outcome.
From testing:
3-2 against PU Dragons. This should have been 4-1, however, as the AI made a playing error when Fractaling Dragons. The other loss was because the AI drew 0 Bone Walls in 19 cards...which isn't exactly something common. Silence is disastrous rarely (even when it is drawn, which was in my starting hand every duel for some reason -_-), but fortunately the lack of CC means we can spam Dragons freely and I doubt they would include CC as it would severely disrupt the quanta balance completely.
4-1 against Immobow. This is harder to gauge as normally I would wait to Fractal Bone Dragons since this deck is covered with CC, but I had to make approximations of whether or not the AI would have been able to kill me had it been patient. For Bonebolt's one loss, the Immobow drew and played 4 Graboids very quickly, which is pretty unlikely. The win margin is probably smaller, but it seems we have the advantage assuming RNG is kind to us.
Are we still not sure of whether or not they have a Fractix hiding in their vault? Otherwise we may as well get rid of that Plague; the decks I played against either won't have creatures or won't make creatures targetable until it goes in for the kill so it will almost be completely wasted.
If Fractix is ruled out then we could swap out a Plague for an Arsenic or something else.
