I don't see anything about you being able to use cards from your account (change decks) and that would be totally different from the last war so please show me where that rule is if it's changed.
what I mean is you can build a deck for the round as if I was going to play it. I have the Nymphs.
example, its vrt vs jdmt
instead of building a deck for vrt we build it based on my card pool.
then when it comes to battle I detail that I will be stepping in for vrt. surprise
kael plays a nymph deck where jmdt didn't think of it
kael wins easily
Later kael vs rastafla
rastfla knows I'm a nymph pimp, and prepares
kael plays a basic deck instead, surprise
kael wins easily again
tactical misdirection
not being able to use upped cards is weak, but manipulating card pools is still valid.