Twin Spell
( Tome and Blood: A Guidebook to Wizards and Sorcerers, p. 42)[Metamagic]
You can cast a spell simultaneously with another spell similar to it.
Prerequisite
Any other metamagic feat.,
Benefit
Casting a spell altered by this feat causes the spell to take effect twice on the target, as if you were simultaneously casting the same spell two times on the same location or target. Any variables in the spell (such as targets, shaping an area, and so on) apply to both of the resulting spells. The target suffers all the effects of both spells individually and receives a saving throw for each (if applicable).
In some cases, failure of both of the target's saving throws results in redundant effects, such as a twinned charm person (see Combining Magical Effects on page 153 of the Player's Handbook), although any ally of the target would have to succeed at two dispel attempts in order to free the target from the charm. As with other metamagic feats, twinning a spell does not affect its vulnerability to counterspelling (for example, using an untwinned form of the spell doesn't negate only half of the twinned spell).
A twinned spell uses up a spell slot four levels higher than the spell's actual level.