100% MAGIC PIERCE?

I know there are posts about m.pierce but the most related is posted in 2017 (maybe the ppl in the thread inactive now)
My question is:
If I have 75% magic pierce (I have 87% currently) and I inflicted [weaken] ailment (-25% mdef) to a boss/enemy, will I ignore ALL of the boss' mdef?
I couldn't find the formula, sorry...

 

I was wondering coz I think it's:
Example boss have 100mdef
Then inflict Weaken ailment (-25%mdef)
Result to 75mdef
Then I pierce 87% of that "75 mdef"...

 

Yes, it works like this. Armor break, weaken and pierce are calculated separately

 

CMIIW, if u got 87% p.pierce, yup it works like that
debuff applies 1st before calculating the pierce u got, so 87% of 75 mdef is 65.25
75 - 65.25 = 9.75 mdef
therefore your enemy should only have 9.75 m.def when you apply all of the above scenario.

 

But I believe the mdef reduction doesn't work on bosses, idk about mini bosses

 

off topic:
@Yunan yo what's up, your still not active in game right now? i miss your m.resist food xD