Arsonist's Oil is an uncommon type of Potion that can coat a weapon with a resistance changing coating.
It was then that Swires tossed the oil. It splattered the cambion, and all at once its skin of brilliant carmine dulled to dark, a red like cheap wine, and the fiend vented this sound of anguish I almost pitied, for its very affinity to fire was now undone.
Properties
Potions
Single Use
Rarity: Uncommon
Weight: 0.7 kg / 1.4 lb
Price: 175 gp
Effect
- Coat your active weapon for
Duration: 10 turns with a Poison that changes the Fire Resistance 
of targets to Fire Vulnerability 
. - Has no effect on creatures that are to immune to Fire damage
.