Summary: Carte is fairly new digital trading card game (dTCG). Especially in US, it has just been released earlier this month after the beta testing. So we will certainly continue to see the game evolve with not only addition of the new cards, but with its game mechanics. One feature they are planning to launch with next update in April is already raising some controversy. The feature is leveling up your heroes.
Detail is still scarce, but we know two things:
1. Your hero will level up as you acquire experience.
2. At level 0, each hero is what we already see. So as you level up they get stronger.
3. The highest level will be 9, but may are locked to 4 levels (0-3).
4. Uncertain if player can back and forth with different levels if one likes certain ability at specific level.
Interesting concept, but this seem to be quite hard to balance. One could potentially argue with this, the user who do not have enough budget using Basic rarity Hero can potentially play against Epic rarity Hero user by leveling their heroes. However, with the same amount of effort or perhaps with money (Experience can be bought indirectly by money), Epic hero will just be as better; hence, not closing gap.
One potential utilization of this I can think of is to limit this in Single AI play, Raid mode and maybe specific online duel but for the tournament and official duel keep the standard card statistics i.e. independent of the level.