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, as well as all items with abilities that deal 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.

Magic spell damage is influenced by magic resistance, physical spell damage is influenced by armor and pure damage is not affected by either. All three underlie damage manipulation.

Spell amplification
Spell damage can be directly amplified. Each point of increases a hero's spell damage by %, which equates to 1% spell damage for every  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 afflicted to allies or the own unit to get amplified.

Spell amplification granting talents
The following heroes have a talent that grants them spell damage amplification.

Besides these, the following heroes have other specific spell amplification talents

Spell amplification granting items
Many items grant their owners a spell amplification bonus, either by increasing their intelligence, or by just giving them a direct bonus. The effects are limited to the item's owner, which must have the item equipped.

Unaffected by amplification
There are certain cases of abilities that ignore spell amplification. It is important to note that those spells cannot spell lifesteal either.

In general abilities related to health manipulation (instantly killing effect, health cost, delayed damage) and regular attacks (cleave, instant attacks) do not benefit from spell amplification. The exceptions to this rule are splash,, and which are still amplified.

Damage dealt by a summon is affected by the summon's spell amplification, not by the summoner's spell amplification.