For the vanilla version of the spell, see Melf's Acid Arrow.
Melf’s Acid Arrow
Level: 2
School: Conjuration
Range: Long
Duration: 1 round/3 levels
Casting Time: 2
Area of Effect: 1 creature
Saving Throw: None
By means of this spell, the wizard creates a magical arrow that speeds to its target unerringly. The arrow inflicts 1d6 points of missile damage, and 2d4 points of acid damage. For every three levels that the caster has achieved, the acid lasts for another round, unless somehow dispelled, inflicting another 2d4 points of damage each round. So at 3rd-5th level, the acid lasts for two rounds, at 6th-8th level, the acid lasts for three rounds, and so on (up to a maximum of six rounds at 15th level).