From The Heroes of Might and Magic III wiki

Class	Earth Magic
Basic cost	5
Duration	1 round for each Spell Power
Level	1st

Increases target allied stack's Defense

Level	Effect
None	Defense increased by 3
Basic	Cost reduced by 1
Advanced	Defense increased by 6
Expert	Affects all allied stacks

[edit] Heroes that specialize in Stone Skin

• Xsi the Necromancer
• Darkstorn the Warlock
• Merist the Witch
• Labetha the Elementalist

[edit] Comments

Stone Skin is useful but wanes in comparison to Shield. However, a unit can become very difficult to take down when both of these spells are in effect. Use Stone Skin when Shield is not yet available. There is no use using this contra Ancient Behemoths as all that added defense is ignored. There are much better spells to use than this one, even though it is far from useless.

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