Beltyn's Burning Blood

Known by some as "Trollkiller," a target of this horrific spell must contain blood and must have taken piercing or slashing damage within the last minute. Using this wound as a point of infiltration into the body, you transform their blood into a volatile acid that bursts into flame on exposure to air.

The target takes 3d6 fire damage and 3d6 acid damage and is Incapacitated by pain. If the creature rolls a successful Constitution saving throw it takes half damage and is not Incapacitated. On its turn, a creature Incapacitated by this spell uses its movement to stumble half its speed in a random direction. While the spell lasts, at the start of your turn in subsequent rounds, the effects repeat and the target can attempt another saving throw.

Creatures who approach within 5 feet of the target or who the target passes within 5 feet of take half the number of dice of fire and acid damage as the original target (rounded up). A successful Dexterity saving throw reduces this damage by half. A creature can only take this damage once per round. 

Using a Higher-Level Spell Slot. When you cast this spell using a spell slot of 5th level or higher, the spell’s fire and acid damage each increase by 1d6 for each slot level above 4th.

Adapted from the AD&D 2nd edition book Volo's Guide to All Things Magical.