So how does TT's Armor Reduction Property Work?

What do you mean claw 15%? If you mean a 15% armor ignore on the claw, I believe that is multiplicative sadly.

Threaten is theorized to be additive, too, as provided with convincing evidence here. Otherwise, with Combat Orders, -16% armor reduction from TT32 and -30% armor reduction from Threaten would indeed reduce by a total of -46% PDRate.

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I borrowed my friend's paladin a few weeks back and used it in zak. But i dont remember the dmg i did. I'll test it again when the chance with someone's paladin. If it 46% on czak it would be 4% dmg reduction which is quite negligeable. My numbers should be very high on czak. I will try my best to test as soon as possible. Kinda busy with other stuff recently .