Aberration Banemagic( Player's Guide to Eberron, p. 86)
You can cast spells that do extra damage to aberrations.
When you cast a spell that damages an aberration, you deal an extra 2d6 points of damage. A single spell can never gain this extra damage more than once per casting. For instance, a fireball deals the extra damage to all aberrations in the area it affects. However, if a 3rd-level wizard casts magic missile and produces two missiles, only one of them (of the wizard's choice) gains the extra damage, whether both missiles are directed at the same aberration or two different ones. If a spell deals damage for more than 1 round, it deals this extra damage in each round. Scrolls scribed by you and scrolls activated by you do not gain any benefit from Aberration Banemagic. The same is true for most other magic items, such as wands and potions. However, staffs activated by you not only use your caster level but also gain the benefit of this feat, if applicable. If the spell allows a saving throw, the DC of the saving throw increases by 2. The extra damage dealt by this spell is either halved on a successful saving throw or negated, depending on how the regular damage dealt by the spell is affected by a successful save.