Spell Damage

Spell damage is all damage which is not dealt by physical attacks. This includes all spells which deal magical, physical or pure damage. Even the damage dealt by attack modifiers counts as spell damage, as long as the effect deals its damage in a separate instance from the attack damage.

Spell damage amplification
Spell damage can be directly amplified. Each point of increases the hero's spell damage by 0.0625%, which equals to 1% spell damage for every 16 points of intelligence. Spell damage amplification of multiple sources stacks additively. The amplification does not only affect spell damage dealt against enemies, it also causes damage affliced to allies or the own unit to get amplified.

Unaffected by amplification
Instantly killing effects are not amplified, neither is the health cost of spells. Besides them, these abilities are not affected by spell damage amplification either:

Amplification granting items
These items passively increase the owner's spell damage amplification by merely having them equipped. They either grant a flat bonus, or bonus through intelligence.

Basic items

Abilities based on spell damage
These abilities have an effect which is based on spell damage.