This redwood arrow smells acrid and feels damp to the touch.

A fountainhead arrow is an otherwise normal arrow designed to be targeted at a point on the ground, a wall, or any other flat surface. If you hit the target area (treat as AC 5), the arrow creates a geyser of spewing acid. Each round on your turn (starting on the turn you fired the arrow), the arrow creates a 10-foot-radius burst of acid that deals 2d8 points of acid damage to all creatures in the area (Reflex DC 14 half). This effect continues for 3 rounds.
A fountainhead arrow can be created as a crossbow bolt for the same price.

Prerequisites: Craft Magic Arms and Armor, Melf’s acid arrow.
Cost to Create: 153 gp, 13 XP, 1 day.