So here is what i found out about my best friend, the mondo DR...
(I try to explain it as good as i can in english, i'm not used to speak english)
First of all, i play warrior. I fight him with 2-hand sword and only switch sometimes to staff when i can't get the illusions away from the real DR.
First thing you should know, at least it is that way the first time the DR uses his shield, it is not dependent to his hp. The first time he activate bubble is dependent to time. Try to deal as much damage as possible to him before he activates shield the first time with help of a summon that put out high dmg (I recommended Quix, AM1000 or Lollohund because they deal high dmg and can stand Miasmas at least once).
This is what will happen until he activate his shield the first time:
-Only normal attack (3 or 4 times)
-Teleport
-2 or 3 seconds after teleport Miasmas and 1 - 2 normal attacks
-A few seconds later shield with explosion
So here is what i do:
-Summon someone to help me deal dmg
-Run onto him and hit him as often as i can and evade his single attacks what is not realy a problem
-When he teleports i charge to him so i can use as much time as i can before his first shield
-Evade his first Miasmas and activate Aegis so his explosion he put out when he activate his shield can't kill me
While he is activating his shield and energyball explosion he summons his illusions (the less hp he has the more illusions it will be, for me the first time its 3 illusions)
The illusions won't move until you trigger them. To do that you have to come close to them (attacking them will not trigger the to teleport to you).
After he summoned the illusions i auto triggered those because i was close to them during they were summoned, remember i used aegis and had not to fear that he kills me (without aegis i would be dead after this explosion).
-Now i bring some distance between me and the DR while Aegis is running out. While i do this i use doom blade on him.
If I manage to get far enough away before the doom blade hits he instantly turns into dark shadow and does nothing from now on. (When he is in the center of the map this does not always work because no matter to where you run, you can't get far enough away from him most times)
But once you put him into this state that he does not attack, use explosion or miasmas its not guaranteed that he will not start to attack again. He will attack again when you trigger him through either hit him with any attack or come to close to him. Always remeber that.
To give you a larger area to move around in i recommend to move the real DR into the lower end of the map. (for some reason he has an preference for the lower corner, this is good since the heal pods are placed in the upper end of the map)
Now you have to try move his illusions away from him by getting close to them without getting to close to the real DR. (you can also hit the illusions with staff without trigger the real DR when they not stand to close to him in case you cant move them away very far from the real DR)
Everytime you accidentally triggered the real DR so he start to attack again, remember to use doom blade and move away as far and fast as you can to put him back to just doing nothing. (Maybe every other ranged attack might work, too. I never tried to hit him from far away with a staff for example, i always use doom blade for that)
Just do that again and again until he's dead. I only have to deal with his illusions twice. The first time he has only 50% hp and summon 3 or 4, then i hit him for another 25 to 30% of his hp so he summons... I did not count exactly but i think 5 illusions. I fight against his illusions 2 times, if i have bad luck 3 times.
This is how to turn him into a harmless sheep.
Some other tips you might know about once the DR is idle:
-Attack the DR only when he's in top or down of your screen, for this use the small gaps between the exp-meter etc. in case you have him on top of you, if he is in the lower section of your screen use the small gaps between your skillsbar, etc. (you can't come close enough to see and attack him left or right of the screen, before you see him he is already triggered again and will attack)
-On the real DR i also use wand most times, lower risk and if you attack him useing shift and klick to shoot in his direction he won't teleport to you, he only use miasmas and explosion. Also you can do the same as i said in the point above to klick him when you see him in these slight gaps between the exp meter or the skillsbar so you can even use skills like for example doom balde
I hope this might help everyone out. I don't know if everyone understood what i mean with these small gaps between the exp meter or skillsbar. I try to put in some screenshots as soon as i can.