With enhanced client you can instantly swap your equipment. Might be slower in 2d client and sure that can cause fast death. When he casts this stonerain you have to be fast and. Be sure to drink the healing not when your are full hp. This caused me some trouble in the first try.I tried again, same disastrous results. I don't think this is possible, for me. I seem to have the same setup, same suit, but some of the tactics mentioned I am simply not capable of. I use the old client, so without these "change my entire outfit in .25s" macros, for instance, when he starts to cast the stone rain, it takes me about 5s to swap rings get my shield off (can be a macro) and drink a heal - but by then I am likely dead anyway, given that he will almost certainly have hit me in melee in that 5s too.
Also, Duncan says that he managed to kill him and was never at risk... I am not sure I believe this. He just hit me for a 120 HP combo (that big Armageddon explosion spell for 86, flamestrike for 34). With 150 HP, I am theoretically alive and at 30 hp, but being able to heal quickly enough before he lands another attack is problematic, at best, and so is never letting myself get below 120 HP, given that he basically never hits for less than 25 at a time anyway. Prior to that, he hit me for a 93 damage single attack, and I swear this attack first knocked my off my dragon, and then applied damage, because I was half a screen away from him when it happened.
Also, I found that paying attention to disco was more problem than anything. If you need to run off, running < 15 tiles away is kind of pointless because by the time you get a close wounds off, chances are he's landed another 25-35 damage attack anyway, therefore entering you into a 0 sum game. But then trying to swap jewels, as stated a pain, and redisco him (at best a 50% chance), swap jewels back in, etc. takes quite a lot of time and concentration.
I would *really* love to take the 20 minutes and watch the video of someone successfully doing this, as in my current state, I simply don't think it is possible for me, not without getting super lucky and him never doing one of his combos that is nearly guaranteed death.
Then did you have parry now in your build. If so you should use evasion as often as possible. And if things get hard run around that 8x8 tile in the middle of my screenshot. Slasher has no line if sight on you so he cant cast spells.
When i said there was no true damger of dying i meant stone rain. When he casted it and i was paralyzed i waited till enough hp was down then used the greater heal pot. And than as soon as i could move i ran around that 8x8 tile and healed woth confidence / close wounds.
Then very important: when you are knocked of your dragon immediately remount. You dont get the dismount debuff so this is possible and essential. You need the -20% dmg reduction for the whole battle. With ec client i always have my mount bar near so i can immediately doubleclick to mount. Just make sure you are not in war mode. You attack your pet instead. I always let slasher attack me so the cursor wont get red.