Note: Another useful tactic (they have a low magic defence) is to use (Elite) Void Knight Equipment, preferably with a Deflector and a good mage robe top. The Arcane Stream necklace is not as important here as the magic damage boost it adds only applies to the target you click on. The other 8 targets do not receive the damage boost from it or your staff, so you would be better off using a necklace with a prayer bonus.