Every card has a cost value which can be seen on the bottom left of the screen when inspecting a card (right clicking on it)


Cost's main use is to balance the power level of a deck, when you make a deck and add cards to it, those cards add to the deck's total cost


The host of a game can choose to change the cost limit as well as card count limits, by default the cost limit is 200, and the card limit is 20, this gives you on average 10 cost each card

• C: 4 cost
  
• R: 5 cost
  
• SR: 7 cost
  
• UR: 11 cost

• No Skill: 0 cost
  
• Discard: 1 cost
  
• Standard: 2 cost
  
• GameChanger: 4 cost

• 1 damage: 1 cost
  
• 2 damage: 2 cost
  
• 3 damage: 3 cost
  
• 4 damage: 4 cost
  
• 5 damage: 5 cost

This means that the lowest cost card you could make for your deck would be 5 cost (common, no skill, 1 damage 4+0+1=5)
and the highest cost would be 20 (ultra rare, game changer, 5 damage 11+4+5=20)

Here's some other fun things I noticed about cost value:

• the UR bonus for the trick skill uses cost value to determine what the "strongest" and "weakest" cards are
  
• all D rank cards such as poison or curse are only increased by their damage cost, (even though they have a discard ability)
  
• the XR rarity seems to be 19 cost, you can gain this rarity from the evolution and challenger skills
  
• the assassin skill uses cost to choose which card to discard, this means that it can be helpful for removing traps or poison from your hand.
  
• the end result of a fusion card does not get extra cost for having 2 abilities (I'm not too familiar with fusion, will need more testing)

Thank you for reading!

This is a part of gameplay that I had a hard time understanding early on, so I wanted to make it easier for the next guy
if you have any additional information that I've missed, or think I could have written any sections better, do let me know in the comments!