From The Heroes of Might and Magic III wiki

Class	Fire Magic
Basic cost	6
Duration	1 Round/Spell Power
Level	1st

Level	Effect
None	Target enemy unit does minimum damage
Basic	Cost reduced by 1
Advanced	Target enemy unit does (0.8*minimum damage -1)
Expert	All enemy units does (0.8*minimum damage -1)

Counters Bless

[edit] Units immune to its effects

• Efreeti/Efreet Sultans
• Fire/Energy Elementals
• Firebirds/Phoenixes
• Undeads

[edit] Artifacts rendering your units immune to Curse

• Pendant of Holiness

[edit] Units capable of casting Curse(after attack)

• Black/Dread Knights
• Mummies