In arena, any and all cards are on the table. Even so, you can often deduce what cards your opponent has based off the way they’re trading (or not trading), and what cards they’re playing (or not playing).
A basic example is, if on turn 4 you have a 4/4 minion on an empty board against a paladin, you could expect Truesilver Champion. If they play a 4/4 minion of their own instead of a Truesilver, you can assume that they most likely don’t have one in their hand.
As the card pool expands, there’s more and more to consider. You cannot play around every single card, but you can play around likely situations. Understanding your opponent’s type of answers is extremely critical.
We’ve all lost to top-deck Flamestrike, and while those tend to stick in our minds, losing to the perfect top-decked answer is quite rare. You cannot play around the top draw, but you can play around the cards you’ve understood your opponent to have or not have.
Anticipate Class Cards
If you’ve ever played arena, you should know to try to avoid playing into Flamestrike on turn 7 versus a mage. People have adapted to this by playing higher health creatures, playing deathrattles, or even simply holding back.
You can apply the same concept to other powerful class cards. Against a shaman, turn 6 Fire Elemental comes to mind. Against a hunter, you should be weary of a possible Unleash the Hounds. Druids have Swipe as a way to reclaim the board.
Once again, while you cannot play around absolutely everything, you can still hope for the best but prepare for the worst. If you’re new to Hearthstone and are unfamiliar with all the cards, at the very least focus on learning which area of effect (AOE) cards each class has.
Mage: Flamestrike, Blizzard, Arcane Explosion, Cone of Cold
Rogue: Dark Iron Skulker, Fan of Knives, Blade Flurry
Paladin: Consecrate, Enter the Coliseum, Equality
Hunter: Multi-Shot, Powershot, Explosive Trap, Explosive Shot, Unleash the Hounds
Warlock: Hellfire, Demonwrath, Shadowflame, Dread Infernal (battlecry)
Druid: Swipe, Starfall
Shaman: Lightning Storm, Elemental Destruction, Forked Lightning
Warrior: Cleave, Brawl, Whirlwind, Revenge, Death’s Bite (deathrattle)
Priest: Holy Nova, Shadow Madness, Lightbomb, Excavated Evil
All Classes: MIND CONTROL-TECH
Press Where it Hurts
If you catch your opponent struggling to answer what’s on your board, you have information you can abuse. Whenever they make an awkward trade, make note of it. I don’t think anyone is happy to trade down in stats.
For example, if you have a Frostwolf Grunt and a Clockwork Knight on your board, and your opponent has an Ice Rager, he really wants to be able to throw his Ice Rager at your Clockwork Knight.
If he has any possible way to deal 2 damage to the Frostwolf Grunt or get through the taunt with a silence, he will absolutely use it so he can get the favorable trade (into your Clockwork Knight).
If he ends up having to trade into your Frostwolf Grunt, you can definitely bet that he doesn’t have a silence or a way to deal 2 direct damage, at least within the boundaries of his current mana crystals.
With that information in mind, you can now take good trades knowing that he won’t be able to easily clean up afterwards. Your Clockwork Knight can go on to eat a Sen’Jin Shieldmasta without fear of punishment. Or, you can keep flooding with cheaper creatures to try to overwhelm him since he had so much trouble finding a way to deal 2 damage.
Arena may seem RNG heavy when compared to constructed, but there’s a lot you can consider to give you that extra edge. The more you can deduce from your opponent’s hand, the more you can formulate a winning plan through smart trading and abusing what they cannot answer. I hope these tips have been helpful and may the odds be ever in your favor.