In Warsoul CCG, the gameplay focuses on balance and strategy. When building a deck, you need to keep in mind each faction's strengths and weaknesses:
Black is strong vs Blue
Blue is strong vs Red
Red is strong vs Black
Additionally you can only have 30 cards in a standard deck. However, each card in Warsoul CCG has a command point value, and the total CP in your deck cannot exceed the maximum CP limit of your leader card.
Rarer cards tend to have higher mana costs and higher CP values. This prevents players from spamming their entire deck with all the rarest cards in game. It is a good idea to keep several common and uncommon cards in your deck, because they are cheap blockers that you can use to stall until you have enough mana to play your rarer/stronger cards. Some runes do allow you to lower the CP value or increase a leader's CP limit, so you can decide to use the runes to lower the CP value and add more rare cards to your deck, or have less cards but use the runes to increase your cards' overall stats.
Some cards also have cardinalities, indicated by dots after their name. So for example, you can only have 3 copies of a card named "Templar***" in your active deck.
Thanks for watching, and hope to hear if you think the deck building mechanics is balanced or not.