I was in the mood to test things out today and someone had recently told me that Marked Target isn't worth using because it's bugged and doesn't provide anywhere near the 75% resist/armor debuff. I remember reading this before (and not really caring) and my own damage tests were consistently giving me a 10% damage boost when using the skill. That seemed kind of small considering the magnitude of the debuff, but then I thought, "This really depends on how much mitigation armor actually provides."

I found that there's a difference of 1 point of damage for every 28 points in armor. I did this by letting a mob hit me with all my armor on, then without the chest piece, then with no armor on at all, then comparing the differences in damage with the differences in armor level. 1000 armor means you take ~35 less damage per attack.

We can then apply this to the Marked Target debuff. Say an enemy has 1500 armor normally. They have 375 armor with the debuff, a difference of 1125 armor. That means you should hit this person for ~40 more damage with each melee attack. If your basic light attack was doing 160 damage, it should now do 200.

Of course, that's strange because that's a 25% increase in damage while my testing against mobs only provided a 10% increase in damage. I'm lead to believe that the mobs simply had low armor and the debuff is clearly more affective against those with higher armor values. For instance, if I have 800 total armor and it gets debuffed to 200, then I get hit for ~21 more per attack. With the light attack at 160 this time, it increases by 13% to 181.

Essentially, the skill seems to work as intended. It also seems to be only marginally effective against targets that already have low armor and much more effective against those with very high armor. The reason it appears to be underperforming is because armor (and I assume spell resist, but I didn't test that out at all) provides a relatively meager amount of mitigation in the first place.

I just thought I'd share what I found since I don't think any posts have been made about this yet. Feel free to make corrections; I certainly could've messed something up.

Edit 1: The main thing I'm confused about, where I may have made a mistake, is why all my skills gained 10% damage instead of an absolute value, regardless of how much the skill normally hits. But, my damage tests consisted exclusively of class abilities and basic attacks. Maybe most/all of those class abilities were affected by spell resist instead of armor, meaning that spell resist works differently. Or maybe it's just because I was fighitng mobs and not players.

Edit 2: Actually, now that I think about it some more. The fact that I got a percentage increase in damage may be the bug, if it is bugged. Either way, at least this says something how armor works.