Energy Gestalt( Complete Mage, p. 42)
You have learned to combine multiple energy effects to great advantage.
Spell Focus (PH) (evocation) , caster level 3rd,
The Energy Gestalt feat enables the use of three tactical maneuvers. In every case, you must deal damage to one or more subjects with a pair of energy-based spells you cast in 2 successive rounds. Acrid Fumes: You cast an acid spell followed by a fire spell. The flames of your second spell turn some of the lingering acid into choking, sickening fumes. Any living creature damaged by both spells is nauseated for 1 round. Those who make a successful Fortitude save (DC based on the second spell) are sickened for 1 round instead. Treat this as a poison effect for the purpose of save bonuses and immunities. Brittle Blast: You cast a cold spell followed by a sonic spell. Any object or construct damaged by both spells takes +50% damage from the sonic spell, because its physical structure has been made brittle by the cold. Improved Conduction: You cast a cold spell followed by an electricity spell. The lingering cold more effectively conducts the electricity, temporarily fatiguing creatures. Living creatures damaged by both spells are slowed for 1 round (as the slow spell). Creatures that make successful Fortitude saves (DC based on the second spell) are fatigued for 1 round.