Venomfire

Venomfire was a transmutation spell that caused the venom within their body to become as corrosive as acid, harming them from within.

Effects
While the effects of venomfire could last for hours, creatures affected by it could resist and negate the damage done to their bodies. Naturally, the spell had no effect on non-venomous creatures.

Casting
The spell required verbal and material components, the latter of which was a single drop of acid.