I just started a new multi-box combo, 2 mages and a priest. I'm using keyclone and running three windows on one machine. I have multi-boxed two characters before(back in the old days before such tools as keyclone) namely a hunter and druid and other combos that I later abandoned. I have leveled a frost mage to 60 before using the standard frost aoe technique.

So I started leveling and began following the cookie cutter specs on my mages in frost and on my priest picking up spirit tap and improved wands with the intention to pick up Imp PW:Shield and Fort or pick up Mind Flay.

So I was tooling around Azeroth with this setup and it seemed like things were going slow. I got Imp Blizzard but could only cast it with one character due to the targeting reticule being mouse driven. I used Mind Flay in conjunction with Arcane Missiles to quickly take down single mobs in between camps of mobs.

Then I noticed something in the priest holy tree...

Holy Nova Rank 1
185 Mana
Instant cast
Causes an explosion of holy light around the caster, causing 28 to 32 Holy damage to all enemy targets within 10 yards and healing all party members within 10 yards for 52 to 60. These effects cause no threat.
Hmm ... AoE damage? AoE healing? No threat!?! I respecced immediately.

I was in heaven the first pull. No more tricky pulls, just shield the lead mage run into a camp and start mashing 1 button: Arcane Explosion | Arcane Explosion | Holy Nova! It was like Blizzard designed this spell specifically for multi-boxers!

Before picking this up I could handle maybe five to nine mobs using Arcane Explosion to AoE. More with the frost technique, but it was slow. After speccing my priest for Holy Nova I was taking 15-20 at a time with little problem and less total downtime.

I am in love with this combo and just wanted to share, as most priest's generally consider Holy Nova nothing more than something to pick up and spam rank 1 to uncover rogues or druids. But for the multi-boxer it is sooooo good.