Carrier attacks are a special type of Weapon qualifier attack. If a Weapon qualifier attack has a damage number and a special effect, it’s considered a Carrier attack. In this case, the special effect will only work if the damage gets to your Body Points; if the damage only hits your Armor Points, the special effect doesn’t do anything extra. Carrier attacks can never provide a beneficial effect to the target; if you would be healed by a Carrier Effect, you instead call “No Effect” as if you were Immune to it.
Example one: Rendal is wearing 10 points of Armor and, due to a ritual magic backlash earlier in the day, has temporarily become Healed by Flame. A Flame Elemental steps up and starts swinging its claws with the call “10 Flame!” Rendal takes the first hit, which takes his Armor Points down to 0. When he takes the second hit, he calls “No Effect,” since you can’t be healed by a Carrier Attack. If the Flame Elemental attacks with a Flame call that’s not a Carrier attack—for example, “20 Spell Strike Flame”—then Rendal would actually be healed by the assault!
Example two: Vorik the Necromancer has turned himself into a foul undead creature of darkness! Unfortunately for him, he gets caught in a melee between one of his death knight guards and some living adventurers. He gets struck by the death knight swinging “5 Wither!” and “5 Chaos!”, both of which he calls “No Effect” to since they’re Carrier attacks that would normally provide him a beneficial effect. After the adventurers strike him several times, hurting him badly, he retreats a few steps and invokes Chaos channeling into himself with a packet, calling “20 Elemental Chaos!” Since this is not a Carrier attack, he’s healed by the foul necromantic energies.
Monsters have some limitations on how they can use Carrier attacks. If they are using claws, their carrier attack must be channeled through the claws. For example, a ghoul with claws and the carrier attack Enfeeble may only swing Enfeeble. It may not swing “Normal.” If the monster can use weapons, the monster may call either the carrier attack or the weapon’s properties when swinging with a (non-claw) weapon. For example, a death knight with the carrier attack Magic and a silver longsword may call “10 Magic” or “10 Silver.” With its claws, it could only swing “Magic.”