Breath Weapon Admixture(Draconomicon, p. 78)
Transmutation [see text]
Level: Sorcerer 8, Wizard 8,
Components: S, MB,
Casting Time: 1 standard action
Target: Your breath weapon
Choose one type of energy other than that normally associated with your breath weapon: acid, cold, electricity, or fire. You can modify your breath weapon to add an equal amount of the energy you choose. For example, a wyrm red dragon whose breath weapon normally deals 22d10 points of fire damage could use this spell to produce a cone dealing 22d10 points of fire damage plus 22d10 points of acid damage. Even opposed types of energy, such as fire and cold, can be combined using this spell. The modification applies only to the breath produced as part of the casting.
When you use this spell to produce acid, cold, electricity, or fire energy, it is a spell of that type. For example, breath weapon admixture is an acid spell when you cast it to add acid damage to your breath weapon.