Quick question, is this deck (or some variant on it) currently dominating in general pvp?
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Because I honestly can't see that deck going all that far outside the constrained rules of the war.
I should also point out that it's a little misleading to describe that deck as "only one loss the entire war". The deck in question was not made until round 5, and it was not used in every round thereafter. Also the 1 loss you report is a best out of three matchup. The deck lost considerably more than just a single game, which is what you make it sound like.
Also of note is that by round 5 team
already had the a sizable advantage over the other teams when it came to deckbuilding. They seized an early lead in vault size, so I really think a large portion of why that deck was so feared was that the other teams simply didn't have a counter to it in their vaults by that point.
Finally, earlier variations of that deck which did not use pandemonium were still successful decks in the war, so pandemonium, while it might work well in that deck, was not the sole reason the deck was so scary.
Once again though, I'm not saying that there are no good decks that use this card. What I'm saying is that those decks are not unduly powerful compared to other well made decks.
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I think the main reason this card sometimes seems so powerful is the same reason dusk shield or fog sometimes seem so strong--it's random. Thus you tend to notice when it totally screws you over, but not when your opponent plays 3 in a row and they all lobotomize your dragon and gp your rustler.