From The Heroes of Might and Magic III wiki

Class	Fire Magic
Basic cost	20
Duration	1 round
Level	4th

Note: Spell duration is NOT increased by any of the spell-duration boosting artifacts (Ring, Collar & Cape of Conjuring).

Affected units attack the nearest stack.

Level	Effect
None	Affects one unit
Basic	Cost reduced by 4
Advanced	Affects all unit's within a 2-hex radius
Expert	Affects all units within a 3-hex radius

[edit] Units immune to its effects

• Efreeti/Efreet Sultans
• Firebirds/Phoenixes
• Giants/Titans
• Undeads
• Elementals
• Golems
• Black Dragons
• Gold Dragons

[edit] Artifacts rendering your units immune to Berserk

• Badge of Courage
• Pendant of Dispassion

[edit] Comments

Most powerful combat spell in the game. Allows you to win against opponents you barely would scratch otherwise. The AI will NEVER cast this spell, tho oddly I've seen Berserked AI units "wait" somehow (the spell is still in effect until something comes within their range, at which point they will attack).