To play the game, you need to have at least one full deck. There are several pre-made decks you can earn by playing The Forgotten Hero story, and there are also themed decks you can buy from the store.
You can build your own decks, as long as they follow the rules listed below. You can also quickly export and share your own deck or import other decklists with the help of deck codes.
As stated above, a deck can range from 50 to 100 cards. Most players prefer smaller decks, as that makes it easier to ensure you will draw something useful each turn.
It is extremely advisable to adhere to a 50-card deck size (75-card for three attributes), as it allows for the most consistency, and as every single card can introduce a weakness to your deck, it is best to have as few weaknesses as possible.
'Milling' refers to forcing the opposing player to discard cards from their deck, as running out of cards will draw you the Out of Cards card, but having a large deck should not be mistaken for a viable approach to this strategy. If you seek to last longer than your opponent in the mill game, play a card like Gravesinger, Journey to Sovngarde, or Skeever Infestation instead, as these cards do allow some measure of consistency within your own deck.
Certain groups of cards work well together. One popular example is Orcs, as most Orc cards provide bonuses specifically to other friendly Orcs in play. Another example, which can be seen in the Warriors of Hammerfell deck is Redguards and Item cards. Each archetype can utilize these synergies to their benefit.
While higher rarity cards generally have better stats or effects, one should focus on card synergy first. A common card can be more useful than a legendary depending on the situation of the game.
Aggro: Aggressive decks focus on doing lots of damage quickly. They usually have lots of low-cost creatures and flood the field with cards. Aggro doesn't care about card advantage, because they aim to win before the opponent's cards become relevant.
Tempo: Tempo decks sacrifice card advantage to play more and/or stronger threats than their opponent. They heavily rely on a good magicka curve. They tend to be aggressive or midrange decks.
Prophecy: Prophecy decks are designed to get everything out of their destroyed runes and the Prophecy effect. This allows them to get more free answers against aggro decks. Depending on the card list, the decks tend to be aggro or midrange.
Midrange: Midrange decks use control in the early game and change to a more aggressive playstyle in the mid game. This results in the deck trying to out-control aggro decks and win by aggro against control decks. Instead of focusing on early or late game, they try to provide consistent power at all stages of the match.
Ramp: Ramp is a special type of midrange where the early game is dedicated to playing cards that give a magicka boost. This allows them to play their larger threats earlier than their opponent.
Control: Control decks focus on playing a longer game. This strategy relies on being able to answer (counter) early threats played by the opponent until more powerful late-game cards can be played. They usually have actions or cards with effects that can destroy multiple cards at once, as well as a few high-cost, powerful creatures to finish off the game.
Combo: Combo decks try to stall the game until they assemble their combo pieces to finish the game quickly.
One example of this would be using Nord Firebrand, Stealer of Secrets, and Mentor's Ring in an action-heavy deck. Stealer of Secrets gains +1/+1 for each action in your graveyard, and Mentor's Ring lets you copy a keyword from one creature (in this case, the Charge keyword from the Nord Firebrand) to every other friendly creature.
The 'curve' is the distribution of different cost cards in your deck. You don't want to have too many high-cost cards in your deck, as those could end up clogging your hand and you not being able to play anything.
You can see each deck's curve in the in-game deck editor.