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This is the main class skill for the Mage in the Kings Bounty series of games.
From which the Heroes 3 series originated.
In Kings Bounty:
"Basic - 1 time, 2 spells per battle.
Advanced - 2 times, 2 spells per battle.
Expert - 3 times, 2 spells per battle."
Quite powerful.
Exactly. I suggested a classic version, but in a reduced, non-overpowered form.