Each card has a rarity that governs the amount of experience needed to level up. Cards can be Common, Uncommon, Rare or Heroic. Each rarity is color-coded in the card's information panel in the game interface. Common cards are green, Uncommon cards are blue, Rare cards are purple, and Epic cards have a special gold and red color.
Heroic cards always have unique, deck-defining mechanics. Overall, Heroic cards are balanced against each other but feel stronger than a non-Heroic card. These Heroic cards will never feel like a bad card in a deck, just as the game is not dominated by whoever has the most or highest level of epic cards. Heroic cards are intended to be low-risk "Let it go and forget" cards with high skill paths to maximize their usefulness.