From The Heroes of Might and Magic III wiki

Class	Water Magic
Basic cost	12
Duration	Instant
Level	3rd

Troops in hexes surrounding target receives damage.

Level	Effect
None	Does (Spell Power * 10 +15) damage
Basic	Cost reduced by 3
Advanced	Does (Spell Power * 10 +30) damage
Expert	Does (Spell Power * 10 +60) damage

[edit] Heroes specializing in Frost Ring

• Adelaide the Cleric

[edit] Units immune to its effects

• Water/Ice Elementals

[edit] Units extra vulnerable to its effects

• Fire/Energy Elementals