From The Heroes of Might and Magic III wiki

Class	Fire Magic
Basic cost	16
Duration	1 round/Spell Power
Level	4th

Target allied stack gains 8 Attack when attacking certain foes.

Level	Effect
None	Effect gained when attacking Dragons, Hydras and Behemoths
Basic	Cost reduced by 4
Advanced	Bonus also gained against Angels and Devils
Expert	Bonus also gained against Titans

[edit] Units immune to its effects

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

[edit] Heroes that specialize in Slayer

• Coronius the Druid