The second-most expensive Helm item available, the Vinling Helmet increases a Demigod's Mana and Mana Regeneration by a considerable amount. However, the less expensive Plenor Battlecrown provides a superior amount of Mana and the amount of Mana Regeneration, thus the proc effect accounts for the extra 1800 Gold. Unless the proc proves especially useful, the Vlemish Faceguard is likely a superior Helm.