From what I know about mitigation, is that each separate part of mitigation will separately lower damage. So 100% mitigation won't guarantee you to take 0 damage.
I've found the maximum Mitigation that you can get in the game which comes to this;
T7 earfthfusion legs = 8% each, so that's 16%.
T7 earthfusion sleeves = 3.75%, so that's 7.5%.
T7 earthfusion BP ( not sure if it goes up by 0.5, or 1% per tier for mitigation, so I'll just use 0.5%) = 5%
so from just T7 earthfusion, you will be looking at around 28.5%- 31.5% Mitigation.
Two Timmies at T1 = 10% , so that comes to 20% Mitigation. I believe timmies increase by 1% per Tier, so that would turn out to be 16% per timmeh which = 32%
The T2 LG 2h crusher gives 20% mitigation, and again I believe it increases by 1% per tier. So that will turn out to be 26% Mitigation.
Finally there is a R15 Stone Pot, which gives 33% Mitigation
So 33% + 36% + 32% + 28.5/31.5% = 129.5-132.5% Mitigation. I haven't included Angelic R5 because with it on, you won't be able to do any damage unless you use a stave, however you could taunt and be a tank... So lets add in Angelic for the fun of it.
Total Mitigation 149.5-152.5% Mitigation
Now for the calculation. I've decided to use 10k damage as my base damage, and work my way down from there, so let's begin.
8% of 10000 = 800
=9200.
8% of 9200 = 736
=8464
3.75% of 8464 = 317
=8147
3.75% of 8147 = 305.5
7841.5 ( rounded to 7842)
5% of 7842 = 392.1
=7450
16% of 7450 = 1192
=6258
16% of 6258 = 1001
=5257
26% of 5257 = 1367
=3890
33% of 3890 = 1283
= 2607
Total damage from a potential 10k hit, will end up at 2607 not including angelic aura.
20% of 2607 = 521
= 2086
Total damage from the 10k hit, will end up at 2086 from all Mitigation possibilities.
So this roughly takes the total mitigation of all damage to roughly 79%, these figures seem correct, but again I may have calculated wrong, or used the wrong values, or I haven't calculated mitigation correctly!
Total cost of this build? probably a few beelion! I suggest only t3 max if you want this build
