From Mabinogi Duel Wiki
Levels play a big part in Mabinogi Duel. There is the player level, your level during a match and there are card levels.
Player level[edit | edit source]
Gained with experience
The experience bar indicates, how far away you are from a level up
Match level[edit | edit source]
directly influences the possible number of actions
a level up also increases the players HP by 30% (???) - maximum HP and current HP.
Card level[edit | edit source]