Most of us may be aware of about the trick, which makes mob farming super easy and fast. Shortly put: Kill/damage mobs before they scale HP against all the characters. I don't know the correct numbers, but if a mob have 1M HP, and you damage it on multiple toons with low damage spell (thus not one-shotting the mob) then the mob will multiply it's HP by amount of attackers. If you dmg it with 10 toons, it may suddenly have 10M max HP and so on.
The scaling affects only the percentage amount, so if your pull spells damage mob down to 50% before the scale, it scales its HP to 50% of 10M, so you'll have to dps only that remaining 5M HP instead of more.
I've been oneshotting mob packs that spawns from portals. I run 10 Havoc Demon Hunters, and whenever the portal spawns mobs, I have the toons aligned the way that I can Fel Rush x10 towards the portal, usually killing the whole pack at once. Then I have time to run away from the portal, align the toons again for next mob pack.. If Fel Rush is on CD, then I throw glaives which is also very strong pull spell when cast by multiple characters. (Fel Mastery, Bloodlet and Master of the Glaives talents help there a lot with the burst dmg)
It's super fast method, I believe at least mages could oneshot burst the packs down with multiple Supernovas, but the CD on that talent might be a bit too long even with 2 charges.
If you have multiple beacons with same colour, you can use one at first to check the location where the portal spawns with that coloured beacon, then just spam all the beacons with same colour on all toons, and you'll have an awesome farming spot for a long time, as the other beacons go to the "queue" and portal just keep pushing and pushing the mobs, waiting to be oneshotted with your team..