D&Dtools1

A horn like a unicorn's sprouts from your forehead. When you complete this spell, you grow a single horn about as long as your forearm from your forehead. As a standard action, you can use this horn to make a single gore attack as a natural weapon. A hit from the horn deals 1d8 points of piercing damage (if you are Medium) plus 1-1/2 times your Strength bonus. The horn overcomes damage reduction as if it were a magic weapon.

Alternatively, you can use the horn in a charge attack. In this case, you deal double damage when you hit, or triple damage on a critical hit.

As a swift action while the spell lasts, you can invoke the power of good. Doing this gives the horn a +3 enhancement bonus on attack rolls and damage rolls, allows it to overcome damage reduction as if it were good-aligned, and makes it deal an extra 3d6 points of damage against any evil-aligned creature of the following types: fey, giant, magical beast, or outsider. This effect lasts for 1 round, after which the spell's duration ends.

If this spell is in effect when you cast unicorn blood or unicorn heart, the combined magic has an enhanced effect. See those spells for details.