First,let’s study how mp absorb an alchemy work. As I read, you first recover and current hp/mp can go over max. After, you take dmg and,if your hp/mp is still over max, it becomes equal to max.

Then let’s see how many DR (damage reduction) we need to recover the same amount of hp/mp as we lose with 20% mp absorb. So, we take 80% of dmg and recover 20% which means we need (0.8-0.2)/0.8 = 0.75 = 75% DR.

Now,how much armor do we need? DR from armor in arena = armor/(armor+ 20 000). We need 60 000 armor for 75% DR.

Flat armor:
300 from natural armor (if+25% quality)
2400 from eternal lederer’s lance (jaspered)
1700 * 5 = 8500 from 5 crystal affixes
1400 from eternal pet
8000 from 16 strength (max) Total: 20 600

armor % (we need 200%):
60 % from 4 endow
18 % from eternal lederer’s lance
18 % from eternal pet
9% * 5 from other items
75% from plagued(3) total: 216 %

Let’s work with the formulas for PVP using the information you provided and
Armor: 20,600 Mp%: Cap at 16% (not 20) Multipliers: 1.75 (1+ .75From Plague), Multiplier: 2.41 from endow, lance, pet, and items (1+.6+.18+.18+.45)
Then Total Armor: (20600)(1.75)(2.41)=86,880.5
Armor reduction: 86,880.5/(86,880.5+20,000)=0.812875
then your total damage reduction is (1 - (1-0.16)(1-0.812875))(100)=(1 - (0.84)(0.187124))(100)=(1 - 0.157184)(100)= (0.842816)(100)=84.2816% Damage Reduction

Just for info: against an opponent with Eternal Bloodless Victory with 19% Armor Piercing the above calculation become Total Armor: (20600)(1.75)(2.41)(1-0.19)=70373.205
Armor reduction: 70373.205/(70373.205+20,000)=0.778695
then your total damage reduction is (1 - (1-0.16)(1-0.778695))(100)=(1 - (0.84)(0.221305))(100)=(1 - 0.185896)(100)= (0.814103)*(100)=81.4103% Damage Reduction

About how critical lowers damage reduction, it not exactly lower but let me explain with a formula: Let say you have 80% damage reduction and opponent get a Critical and he have 50% Critical Damage. If opponent get a critical against you you will get: (Damage)(1-0.80)(1+0.50)(100)=30% Damage
If opponent get a normal attack then you take: (Damage)(1-0.80)*(100)=20% Damage, as you could see is like a critical lower damage reduction since you take more damage.

When i go to reach on top3 but little warrior deffend he’s (AI) work i do not expect that but he’s IGN ZURCRAM it’s so nice and good combination with your build sir.