Energy Substitution( Magic of Faerun, p. 21)
You can modify a spell that uses one type of energy to use another type of energy.
Knowledge (arcana) 5 ranks, Any other metamagic feat,
Choose one type of energy: acid, cold, electricity, fire, or sonic. You can modify any spell with an energy designator to use the chosen type of energy instead. A substituted spell works normally in all respects, except that the type of damage dealt changes. For example, an acidic fireball still deals damage in a 20-foot spread, except that it is acid damage instead of fire damage. If a spell has a secondary effect, the altered spell still has that effect. For example, a shout spell can deafen creatures and deals extra damage to crystalline creatures; if fire is substituted for sonic energy in a shout spell, creatures can still be deafened and crystalline creatures still suffer extra damage. Sometimes a spell's minor effects are directly related to the spell's energy, for example, a flaming sphere can set items afire, but a purely sonic or acidic flaming sphere does not. When a spell deals some damage that does not come from energy, Energy Substitution does not affect that portion of the spell. For example, ice storm deals 3d6 points of impact damage and 2d6 points of cold damage. An electrical ice storm deals 3d6 points of impact damage and 2d6 points of electricity damage. A substituted spell uses a spell slot zero levels higher than (the same as) the spell's actual level.
You can gain this feat multiple times, each time applying it to a different type of energy.