BIG TIP

Have as few cards as you can, usually removing or upgrading every starting card by the end round is something you should be striving for. The less cards, the better odds you get what you want. I aim for 9 max. Having less than that is even better. You wont be helped by getting 2 block or doing 2 damage on round 12. However you will be hurt severely by drawing those cards on round 12. Also remember you do not need to pick a card after every round. If none of them fit with your strategy, don't take them. I usually only pick a few if they give me something I want or something that is one upgrade away from a card I need. Using the 2 cost upgrade where it lets you pick from attack, skill, or influence cards is another one I use several times a game and helps with this process. RNG, no thank you.

EXPANDED UPON FURTHER (REDUNDANT BUT IMPORTANT)

Really I cannot stress enough how much removing cards from the deck helps in this game. With the warrior there are two free cost card called Camaraderie and Arsenal that lets you draw one card, if you have your entire deck in your hand (say its six cards) and one is a free cost damage and one is Camaraderie you can literally do those cards back to back forever. There are combos you can do with the Rogue to make cards free as well, or if you use the build I recommend, being able to draw the entire thing so you always just draw what you just played is SO effective. Having 10+ random cards and four you really want to open with is useless. Having seven cards with four you want to open with is guaranteed success. Quick Maths.

DESTINATIONS

In my opinion the best destination choices are The Smithy (for upgrades) and The Sage (for removing cards), second best choices are Corpses (random cards), and The Hideout (in Multiplayer only - you can gift your team-mates one gem, and as long as everyone does it, you all get two. It even works with two people). Next Tier would be Ruins (gamble 1 for 3, when it works it's great, when it fails three times it's not so great) and the Armory (it has a random card upgrade). Only grab a Camp if you need to heal, and if you want to play with Artifacts you can, but there's only a few that are useful in every situation.

ARTIFACTS

No Brainers:
Silver Spoon - one or two gems for three gems
Torn Button - minus 2 HP for plus 8 HP

Early Godlike Artifacts:
Whale Figurine - one extra gem after each round, clearly amazing to get early
Golden Ticket - pays for itself if you have good destination choices coming up

Other OK Picks:
Loot Crate - helps in fights by extending first turn
Kielbasa - lowers cost of a starting hand card to zero

Everything else is more situational, there are other good ones I didn't mention, but these I look out for on every play through no matter what character.

WARRIOR

The Warrior is amazing and if done right can solo the game. they have access to incredible draw power and incredible damage. The cards I recommend focusing are Mighty Weaponry, Fury works too if you have to, and Crystal Sword. Mighty weaponry hits for 12 in a wide area, for only 1 cost. Now you need to pair that damage with draw power. Keep or upgrade into as many copies of Battle Juice as possible, I like to have two copies of Second Wind and have at least one copy of Camaraderie, Arsenal, or The Collector. Tactics is ok for this but out shined by other cards that do it better. Arsenal is probably the favorite since it helps everyone, as long as you play it AFTER you play Second Wind to build some Stamina.

Special shout out to Scythe, which kills all monsters with 10 or less in a medium radius, for 2 cost, meaning you can do more, cheaper, with Mighty Weaponry, but still, if you only managed to get one copy of Mighty Weaponry and the game hands you Scythe, it's not a bad choice.

As tempting as it is to bring in free damage spam cards like Flurry of Blows or Shadow Sword this can get you killed with monsters that return damage, and quickly fill your deck reducing your turn to playing 5 copies of Shadow Sword for 15 damage which is pretty terrible. If you want to build the BLOCK BOI BUILD I personally find it hard to get together properly. Getting some block build cards will NOT have any synergy with the strategy I am about to explain. The only acceptable one would be Team Effort, and only at one copy.

With the draw/damage strat all you do is juggle between cards that let you draw and get more mana, and play cards that can wipe huge chucks of the board out for 2 or 3 cost. This is best paired with a mage that also runs lots of draw power. If a mage plays equilibrium you get 2 cards and 2 mana, if they play Weave Laylines, even better. If you can get a deck consisting of 6 to 8 cards and two or three of them are Mighty Weaponry, one or two copies of Second Wind, and one Arsenal, you should be set.

Example: Open with Battle Juice, hit an area with Mighty Weaponry for 12, play Second Wind, do 12 damage again, use Arsenal, everyone draws 3, 12 damage again, Mage uses equilibrium, do 12 damage again, twice, end turn. That's basically half the end board finished by yourself, if your team is competent that should be a one turn (assuming you got round robin as your debuff ofc).

ROGUE

The best build imo for the Rogue is the gems build, where you get as many copies of Shakedown, Trickle Down, or Stonks, all of which do twice as much damage as how many gems you have, as you can. So obviously, figure out what cards turn into those, and try to spend as few gems as possible and if you can, ignore the gambles, do triple gift, buy silver spoon relic, whale relic early is godlike.

Using Overexertion, Rallying Cry or Finesse is good too since it just increases how many gem damage cards you can use this turn. Everything else should be removed if possible. Anything clogging your deck up that doesn't do gem damage or get it to you is a dead card. It should be fairly easy to get two Shakedowns by turn 5 or 6 and have 5 gems for 10 damage. By endgame you want a minimum of 10 gems for maximum kill power. The more the better. You will be the ultimate damage if you have Stonks in your deck and 15 gems. Even if your team mates are't focusing draw-power (which would be wild imo, unless you have a three rogue team).

You can use Stonks or Trickle down to hit for huge numbers in an aoe for 2 cost each, or Shakedown a single target for one cost. Using Rally-Cry or Overexertion first will make them cost zero mana, so with an obvious task ahead to get as many damage cards in hand and hopefully make them free there's nothing stopping you from killing the final boss with 5-6 cards played. Battle Snack is also a pretty good card, even though it ends up not doing much, but you can free heal yourself with it repeatedly which is nice. It has Strain so it costs more with each use which is why I don't really recommend it because it's not worth it after the first use.

MAGE

The game seems to lead Mages into trying a deck that plays off of having Status Cards in your deck, do not attempt this unless you are a strong player, it's very RNG dependent at all stages, moreso than usual that is.

The best role for a mage is being the king of free cards and mana for the team. They are equipped with the best tools in the game for this. First of all Weave Laylines, 5 mana, 2 cards, whole team, and at zero cost. Having one is great, two is amazing, three is overkill. The best card you can have in your deck is called Equilibrium, learn what turns into it, and get them whenever possible. One cost, all players get 2 mana and 2 cards, unlike Laylines though it has Strain instead of Exhaust. You can play it for one and get two mana. Then again two for two later. It only becomes "cost prohibitive" at three cost or above. By that point you should have done enough damage as a team that it's ok to have it be dead or just play it anyway for 3 if you feel like it. Playing it at 3 costs you 1 mana total to do, but gave your team a total of 4, so still, it's incredible. As soon as I saw this card for the first time I said aloud "Oh my god, the best deck in the game would be like two copies of Incantation (which grows slowly into Maelstrom which hits for 15 and freezes in a huge radius) and as many copies of Equilibrium as possible." I eventually made something close and can confirm it's insane. Another great draw card is Arcane Wager, it draws 4, so if your deck is thin play some cards first to make sure you can actually draw that many. It's a free cost draw that can also return more mana than it cost to play depending on what it draws. If you can get one, do. One is usually enough though.

As far as damage, aside from building Maelstrom, which isn't the easiest or most reliable strategy, you can try to get two copies of Meteor, it's not the best damage in the game, but it's good. Another strategy I have tried is if you can get a copy of Triage, which heals you for a huge amount, get some copies of Blood Surge, that hits for 15, but hurts you for 4. There's Channel Pain that works as well in this strategy, but it's VERY dependent on you being able to heal yourself by something like 12 HP a turn, which is only really possible with Triage. Which makes this strategy a hit or miss, and something to go into only if you have an easy in into Triage. I think the only card that upgrades into it is Simulacrum. If you can get one, you can get a Triage, and I would recommend trying it at least once.

The Magic Bolts, over-all aren't great, harpoon bolt is OK, but it's hard to get anything that low without killing it already by the end stages. Damage cards I like to have at one in the deck are Fractal Whip or Outburst. Outburst is more situational since it's near range only, but could potentially do 60+ damage easily.

Personally I think it's easier to focus specifically on getting a strong draw engine going, and try to get a few freeze cards like Chilly Blow and Rune of Ice. I don't recommend the frost support cards, the bolt damage to frozen influence cards seem to make sense, but there's so much better.

It's very easy to be scrappy and still pull together a super helpful Mage deck. With some Equilibrium and Freeze cards, even if the rest is a bunch of one offs, you can still be incredibly useful doing mitigation and draw plus mana for the whole team. If you lost at that point, I argue it wasn't on you.

I promise you this game is not hard, I haven't been playing more than like 50 hours and I really need to get busted on by the RNGesus to not win a game. Best of luck out there I hope this guide helps!

Edit: The game has received some patches and this guide is no longer 100% accurate, however the basic premises should still be helpful.