Hero's Combat Mastery

How does this skill work? What exactly happens when 40% of a monster's defense is ignored? Is this pertaining to weapon def or PDR?

It is currently believed that mob WDEF does not apply to damage calculations anymore. Only PDRate/MDRate matter.

So, Combat Mastery had better refer to PDRate.

Just exactly how this skill works is not entirely clear to me. The options are
1) Monster's PDRate is reduced by 40% (i.e., becomes 60% of what it used to be), against said Hero's attacks. So for example if Pink Bean has 70 PDRate, against maxed Combat Mastery it only has 42 PDRate. This is the most straightforward reading of the skill description.
2) Monster's PDRate is reduced by 40 (linear, or additive). To take the PB example, its PDRate is reduced from 70 to 30. This is the most "optimistic" interpretation, and I personally think it's too good to be true, but Nexon has been known to add percentages instead of multiply them, so who knows?
3) Monster's entire PDRate is ignored, 40% of the time. This results in the same DPM as (1) on high-hp mobs (bosses), but in inconsistent damage on normal training mobs. I don't see how the skill description can be read this way, but descriptions are sometimes really badly translated, and someone posted it on another thread, so I'm repeating it here for completeness.

Edit: started testing, on low PDrate mobs: White Fang, PDRate = 5
My damage range is 9290-13272 and I was using normal attack.
Theoretical damage using option (1): 9011 - 12873
Theoretical damage using option (2): 9290 - 13272 (5-40= no defense at all)
Theoretical damage using option (3): 8825 - 13272
Observed damage: 9020-12851

So, option (2) is ruled out by the lows.

No way of completely ruling out (3), since its range is wider than (1)'s, but I will try this on higher PDRate mobs and if I can't break out of (1)'s range over a couple hundred attacks I will consider it correct.

So, Combat Mastery had better refer to PDRate.

Just exactly how this skill works is not entirely clear to me. The options are
1) Monster's PDRate is reduced by 40% (i.e., becomes 60% of what it used to be), against said Hero's attacks. So for example if Pink Bean has 70 PDRate, against maxed Combat Mastery it only has 42 PDRate. This is the most straightforward reading of the skill description.
2) Monster's PDRate is reduced by 40 (linear, or additive). To take the PB example, its PDRate is reduced from 70 to 30. This is the most "optimistic" interpretation, and I personally think it's too good to be true, but Nexon has been known to add percentages instead of multiply them, so who knows?
3) Monster's entire PDRate is ignored, 40% of the time. This results in the same DPM as (1) on high-hp mobs (bosses), but in inconsistent damage on normal training mobs. I don't see how the skill description can be read this way, but descriptions are sometimes really badly translated, and someone posted it on another thread, so I'm repeating it here for completeness.

Edit: started testing, on low PDrate mobs: White Fang, PDRate = 5
My damage range is 9290-13272 and I was using normal attack.
Theoretical damage using option (1): 9011 - 12873
Theoretical damage using option (2): 9290 - 13272 (5-40= no defense at all)
Theoretical damage using option (3): 8825 - 13272
Observed damage: 9020-12851

So, option (2) is ruled out by the lows.

No way of completely ruling out (3), since its range is wider than (1)'s, but I will try this on higher PDRate mobs and if I can't break out of (1)'s range over a couple hundred attacks I will consider it correct.

Im pretty sure it's option 2 and you're doing it wrong.

EDIT: i misread your options ignore me for now.