From The Heroes of Might and Magic III wiki

Class	Air Magic
Basic cost	25
Duration	Remainder of the battle
Level	5th

Summons Air Elementals. Only one type of Elementals may be summoned each combat.

Level	Effect
None	Summons (Spell Power *2) elementals
Basic	Cost reduced by 5
Advanced	Summons (Spell Power *3) elementals
Expert	Summons (Spell Power *4) elementals