The way I see it, if we assassinate a team that gets decimated this round, it's not going to help us that much in the long run. Whereas, being able to salvage 2 aether cards from an opponent could potentially be huge later in war.
I would like to choose
for spy because we know they have fractals and dims. But I am not confident in this matchup atm.
Let's list opponents, what we would steal from them, and the chance of success.
Stealing their in-element cards would probably break them more, and stealing cards of our lost decks can help us.
Stealing our in-element cards can also help, but we have enough, don't we.
I would steal weapons or other rares
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Like: light - miracle, sanctuary - we have 2 light decks and light seem to be beatable - cards worth to us better than medium
entropy - discord, explosion - lowering the overall discord count, an upped discord may work in nova decks, explosion is on our side - cards worth to us lower than medium
time - dims, fractal (deuce) - i agree that it is futile to steal eternity from time, and useless to us steal pharaoh. - cards worth is better than medium
air - OE, vamp dagger - they lost one deck to us, but they could rebuild it. we could use a copy of both of these - cards worth is better than medium
fire - you can steal dims, fractal here to attempt to ruin their fractix - this would limit their lt/gen deck choices.