Master of Elements
Every time a friendly stack dies, a group of elementals enters combat at the hero's side. The number of elementals increases depending on hero level. In addition, Summon Elementals and Summon Phoenix spells cast by the hero are more powerful.
I have a question about the second part of his ability. Does it really make Summon Phoenix/Elementals stronger? Or is it just information that he starts with Master of Conjuration so those spells are improved from the start?
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I'm pretty sure it works as every other spell special (either from hero or perk) and raises the effective spell power (i.e. +4 spell power) when casting one of those spells.