Flames of Phlegethos

Flames of Phlegethos was a spell used by warlocks of the late 15 century DR, particularly those who forged infernal pacts.

Abilities
The warlock summoned from the plane of Phlegethos streams of liquid fire, with which they doused a target within, burning their flesh and anything flammable. Even if the creature survived the initial onslaught, the flames continued to burn until put it out.