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This is a very useful skill you'll obtain after switching to Magic Knight class. Players in PvP mode often use this technique to stun their enemy, making them vulnerable to skill attacks or combo. This type of attack also works on monsters to canceling any skill cast or make them flinch to make them open for any combination.  Fireball Dash unleashes a huge fireball skill after running. To execute this skill, simply double tap the arrow button toward your enemy, and while running, press Z, Z, X. When you press Z, your character will slash the opponent after the dash, hitting them twice with 120%–160%. Pressing X will execute the fireball within the combo, unleashing 270% magic damage. Aerial Fireball is another approach in releasing Fireball attack. This occurs when you jump to avoid any opponent then unleash Fireball while in mid-air. To execute this combo, run toward the enemy by tapping the arrow button and then jump by pressing up, followed by X and Z. By the time you jump and pressed X, your character will swing his sword, damaging any enemies who attempts to jump with you, causing 200% physical damage. At Z, you will release your Fireball, which will cause 200% magic damage. This is best done with fast combo execution. As Magic Knight are great with mid-range attacks with their Fireball skills, enemies will attempt on doing more close-range attacks to prevent you from doing more Fireball combo.  Most enemies will now dash toward at you then slash before you could swing your sword. To prevent this, use the Knockback Slash to knock them back, making them fall to the ground and vulnerable to your next combo. Simply tap on the arrows twice toward your enemy's direction to run and then press Z after the dash, followed by two more Z to attack. The first slash will inflict 120% damage if you manage to land a hit on your opponent. 160% for the second attack and 200% physical damage to the third. This combo also works on some boss. Use this skill to your advantage, for this increases your chance in surviving the game.
Use Fireball. Use Knockback.