Okay so I was asked to post any strategy info on the duels this round that I'd come across.
FIRE:
They have a lot of options they can throw at us, so they require the most attention and calculation when playing against them. There's a lot that you can deduce from the starting mark, so pay attention to these few factors:
1) Earth mark. This either means you'll be facing an EQ deck or a Graboid Rainbow of some type. Unfortunately if you go 2nd then you likely won't find out which one it is until it's too late. Against Grabbows you're going to be pressed to push out every last bit of luck you've got in you because at the end of the duel the winner is most likely going to be determined by whose draws are the most fortunate. BB their creatures, not yours, and spam Frogs ASAP. I still advise playing your Pillars/Pends ASAP even if you're playing your first game. Their EQ Golem decks are not very threatening, surprisingly. ImmoGolems + EQ is a bit scarier, but the main issue is this: They have to add at least 3-4 EQs into their deck in order for them to be able to use them effectively. This in turn takes away from their offensive power and slows them down a bit. Facing off against Pends makes them play Golems at a snail's pace and makes the duel incredibly easy for you. Use BB on the opponent's creatures; aside from Rage Potion there's not much for you to be concerned with.
Note that because I don't have access to (nor have I tested against) every type of these decks imaginable, you might have to adjust your playing strategy in the middle of the game. For example, if you see the opponent nail every single one of your Frogs that you put out during the first duel then that's probably a good sign that you need to protect them next game. The first game gives you the advantage of learning their deck and forming a counter against it; just be aware that they'll adjust against yours as well.
2) Aether Mark. This either means you'll be facing Fractix, PU Phoenix, a Dim Shield deck of some type, PU Dragons, or a Fire rush with Lightnings splashed in. Fractix I can almost guarantee will never be used against us with access to only 3 upgrades, and even if it does, EQ gives us a significant advantage to allow us to outrush it. PU Phoenix is more likely, but EQ again gives us an enormous upperhand. Should be easy to just outrush. Dim Shields are a bit scarier, but with some timely EQs we can get around them just fine. CC will likely be low in a deck like that since there's no need for it when they have Dim Shield. Lightning splash is another simple deck. It has the potential to be deadly, but EQ and BB on your Frogs before BBing anything else should prove to be beneficial. PU Dragons is about the same as PU Phoenix: dies to EQ.
3) Light Mark. Firesancstall. Pray for EQs in your starting hand. BB your Frogs and Adren them as soon as possible. Ideally you should focus your EQs on Fire Pends first because otherwise they'll have the ability to play more Sanctuaries and Miracles after that, but there will be cases where having the opponent generate ridiculous amounts of
is going to be a very, very bad thing so it'll mostly be your call based on how the game's going. Fire Shield is slightly problematic, but you can BB your own Adren'd Frog Multiple times to save it from getting killed if you need to. Won't be the same as facing an AI where the AI will spam as many Fire Bolts on your Frog as possible without bothering to generate more quanta, so you'll need to be wary of this as well. Fahrenheit is mitigated by EQ, so it's not too pressing of a concern for you now.
4) Death Mark. Fire's variant of Bonebolt. Easy win, especially with EQ. All you need to do is BB your Frog, Adren it, get rid of as many Pends/Pillars as possible in the process, and then watch the rest unfold. Bonewall is laughable and Skull Shield will have hardly any impact against BB'd Frogs.
5) Air Mark. This is one of the scary ones. Even if you EQ their Pends ASAP, it will only take 4 turns for them to gather the quanta they need to play Wings and then stall you for...ever. These decks will likely come with Sky Blitz, so your best chance is to BB the Dragons when they appear and then hope that they stop drawing Wings to continue the chain. I doubt they'd bother packing Shockwaves in this type of deck.
The rest of the decks shouldn't be too threatening. Steam Machines are probably the only deck that might be threatening, but with EQs AND BBs these should fall pretty quickly.
DARKNESS:
I don't really know what to expect from these guys. Devtal spells trouble, but I really doubt they'll bother taking it against us. Their Grabbows are fairly slow by Grabbow standards, so I doubt you'll have trouble winning the damage race. Jade Shield stops Minor Vamps from countering your Poison as much and stops the threat of Drain Life. Stealing Arsenics is going to be problematic, but you'll likely figure out what deck you're facing by the time you've finished your first duel anyways. I haven't done much testing in this matchup so I can't really say anything more constructive.