He is not exactly a new class, but considered as a “gaiden” character, outside of the main class system. Enter the Dark Avenger, an advocate for the Fire element who specializes in AOE and short-range damage. At level 50, he gains the skill to enter the “real” Dark Avenger mode. Dark Avenger must be created as a new character, and has no access to any other classes.
Just to note, the “Dark Avenger” mode is temporary. Here is how it works: Dark Avenger has a skill which provides him with 10 “Avenge” status. At level 50, when using “Dark Avenger” mode, 1 “Avenge” status will be consumed every 2 seconds. The active dodge ability will not have cool-down, but consumes 2 “Avenge” status. Dark Avenger’s basic attack gives 1 status upon each fatal kill.
As you would have guessed, the Dark Avenger controls the power of darkness, or black flames if you would. In “Dark Avenger” mode, the damage dealt is now significantly higher along with better mobility and increased fatal kill rate, while retaining the Fire element damage party buff from his Avenger skill tree. This slightly “messy” character is supposedly aiming the more veteran players.