"Our sorcerer threw everything he had at that druid. Nothing worked! Not even that Fireball that wiped out the rest of the druid's army."Anti-magic is a third-level nature magic spell in Heroes of Might and Magic IV that costs five spell points and makes the target immune to all spells for the duration of the combat.
A powerful, though double-edged, weapon, anti-magic basically acts as a continuous Dispel on the target. Any spells on the target are dispelled (including potion effects) and the creature is subsequently completely immune to all spells - friendly and hostile, like the black dragon's "Immune to Magic" ability. It also effectively dispels all the spells already cast on the target creature.