This isn't a repost as far as I know. But it does make for quick runs from Iskatu all the way to Rakanoth while staying in Archon form the entire way to him then of course killing him in Archon form.
Ok setup I use:
Archon - Teleport rune
Hydra - Venom Hydra
Energy Armor - pinpoint barrier
Magic Weapon - Force weapon
Right and left click can be anything since you prolly won't use them much.
now the explination is quite simple Select the quest Fall of the High Heavens and enter the iskatu encounter I run to the right and lay a hydra to where it will be behind me, then I hit archon form and face the center of the room. Begin blasting away as many Shadow spawns as you can before iskatu spawns. Your DPS needs to be decent so that you can nuke Iskatu to half to make him TP back to mid before he hits you to much. When he teleports clear all the Shadow spawn that you see. then finish iskatu.
Now quickly move through to the next area (using teleport every CD) and start killing everything. Your archon form time will decrease slowly since you have killed over 100 creatures you will have lots of time on it to clear the next area. Teleport every chance you get and just continue to waste every mob you see on the way to the library of fate. Depending on mob generation you might run out of archon form JUST before the library but due to being in archon form for over 2 minutes you can pop it again and just kill Rakanoth.
this works cause of how Archon reads currently. When killing an enemy in archon form you gain 1 second to the duration. It starts at 15 seconds but does not cap at 15 seconds. The more monsters you kill the longer you can draw the duration out for. So if you want to teleport away from iskatu a bit to kill more spawn for more time you can. Just watch your health.
Hope this helps. I have been clearing these 2 bosses in very fast times looting and restarting. My friend is using it to level also. he gains 3-4 bars per run and he's in his 40s.