Dual Wielding Mastery, from what I tested so far

[The Secret Cow Level]

Dual Attack Mastery properties

Level	reserved2	reserved4	reserved6
1	40	400	70
2	42	500	75
3	44	600	80
4	46	700	85
5	48	800	90

Where:

• reserved2: When using attack skills, offhand weapon base damage applied at reserved2 % (before another unknown reduction down to about 80%)
• reserved4: When perform normal attacks (not attack skills), off hand attacks have a reserved4 / 10% chance of dealing full damage.
• reserved6: When perform normal attacks (not attack skills), when off hand attack fails the full damage chance check, the offhand minimum base damage will be randomized between reserved6 % and 100%

Not tested with magical weapons.

Level of mastery:

• Scouts have level 1 DW mastery
• Rangers and Gladiators have level 2 DW mastery
• Assassins have level 5 DW mastery

[Neleth-KT]

I believed ranger has lv 5 dual wield mastery like assassin ? no ?

[The Secret Cow Level]

Damn, can't edit my first post.

Dual Wielding Mastery passive skill is named the following in-game:

• Advanced Dual-Wielding I
• Advanced Dual-Wielding II
• Advanced Dual-Wielding III
• Advanced Dual-Wielding IV
• Advanced Dual-Wielding V

Corrections regarding the reserved6 value, it should be:

• When perform normal attacks (not attack skills), and when off hand attack fails the full damage chance check (chance (1000 - reserved5) / 10%), the pre-defense total damage will be reduced to reserved6 percent.
• When normal attacks lands a critical hit, the final critical damage (applied after defense) is have a further (1000 - reserved5) / 10%) chance of being reduced to reserved6 percent. This means, roughly, that the random damage reduction can be applied twice on critical hit offhand damage.

This means:

• Gladiators and Rangers, due to their DW mastery level 2, each of their offhand attacks have 50% chance that their pre-defense total damage will be reduced to 75%. Roughly, without factoring in enemy physical defense:
  • For normal hits, 50% chance of dealing full damage, 50% chance of dealing 75% damage.
  • For critical hits, 25% chance of dealing full damage, 50% chance of dealing 75% damage, and 25% damage of dealing 62.5% damage.
• Assassins, due to their DW mastery level 5, each of their non-critical offhand attacks have 20% chance that their pre-defense total damage will be reduced to 90%. Roughly, without factoring in enemy physical defense:
  • For normal hits, 80% chance of dealing full damage, 20% chance of dealing 90% damage.
  • For critical hits, 64% chance of dealing full damage, 32% chance of dealing 90% damage, and 4% chance of dealing 81% danage.