This is what I found to be the most effective strategy on HEROIC after countless times fighting this guy:
First off this is suppossed to be a long, easy fight. Your going to want to do MINIMUM dps until about 30% when he starts the arcane explosion or whatever its called. The less dps you do the less adds he spawns. What we did is let the tank take him by himself pretty much down to 45% and just threw in a few ranged every now and then. This actually FORCES the adds to spawn one at a time beginning when Vellaxus hits 85%. And you will notice that they spawn ALOT less. Also if you have a warlock in your group have him/her use their voidwalker to take the adds. The voidwalker will absorb the debuff then the warlock can sacrifice him for the bubble then resummon and repeat:-). Also the hunter pet work's nice and the mage/ice block strat as well. But I found the Warlock/VW most useful as no party members take dmg from the debuff and the bubble actually protects the lock a little bit. When Vellaxus is down to about 30% or so he will start an Arcane explosion which does massive dmg to all party members so at this point you really want to max out dps to take him down quick. All in all the fight should last about 7-10 minutes. Keep in mind some groups are able to all out dps the entire time and still take him down, but this strategy is the easiest and most repair friendly;). Anyway I really hope this helps you out so you dont have to wipe ten times on this guy because believe me I know the frustration.
First off this is suppossed to be a long, easy fight. Your going to want to do MINIMUM dps until about 30% when he starts the arcane explosion or whatever its called. The less dps you do the less adds he spawns. What we did is let the tank take him by himself pretty much down to 45% and just threw in a few ranged every now and then. This actually FORCES the adds to spawn one at a time beginning when Vellaxus hits 85%. And you will notice that they spawn ALOT less. Also if you have a warlock in your group have him/her use their voidwalker to take the adds. The voidwalker will absorb the debuff then the warlock can sacrifice him for the bubble then resummon and repeat:-). Also the hunter pet work's nice and the mage/ice block strat as well. But I found the Warlock/VW most useful as no party members take dmg from the debuff and the bubble actually protects the lock a little bit. When Vellaxus is down to about 30% or so he will start an Arcane explosion which does massive dmg to all party members so at this point you really want to max out dps to take him down quick. All in all the fight should last about 7-10 minutes. Keep in mind some groups are able to all out dps the entire time and still take him down, but this strategy is the easiest and most repair friendly;). Anyway I really hope this helps you out so you dont have to wipe ten times on this guy because believe me I know the frustration.