I believe it aired on Nicktoons or Cartoon Network back in 2012. I did my digging and the two strongest candidates are Dinosaur King and Duel Masters. The scene I remember clearest is the main character getting into a fight with what looked like the antagonist group, and he created a fire card out of nothing. Even the antagonist says "oh, a fire card" or something. They use a device that looks like the one in Dinosaur King. Any thoughts?
Is that Tai Chi Chasers? It has the main character using a fire card.
Tai Chi Chasers is set in a fantasy world that is influenced by East Asian mythology. Within this fantasy world, two ethnic groups, the protagonist Tigeroids (Korean: 호족) and the antagonist Dragonoids (Korean: 용족) are engaged in a long-running armed conflict over Tai Chi cards, a set of 500 magical artefacts that both groups seek for their own purposes.
The plot revolves around the main character Rai, a child who discovers that he is descended from the Tigeroids after his community is attacked. He therefore possesses various magical abilities that all Tigeroids possess. Rai becomes a combatant in the Tigeroid armed forces, and enhances his magical abilities. He also becomes a member of an elite group of combatants, known as the Tai Chi Chasers.
Tai Chi Chasers utilizes Korean hanja to represent the various magical abilities and artefacts present throughout the series. In the English language version, distributed by 4Kids Entertainment, the hanja characters are referred to both by their Korean pronunciations and their English language translations.
The enemy does not say "Oh, a fire card", but he does note that it is a "Tai Chi card" and that it is impressive that Rai can produce and use it would an "Activator".
It was broadcast on the South Korea Cartoon Network channel, although it looks like it was distributed by the CW in the United States.