Two is not an evil number in all systems of numerology, as pairings or opposites are not evil in all systems of mythology.

There are (unsurprisingly) two kinds of pairings represented by the number two. As PureDoxyk suggests, one of these is the God/Satan or spirit/matter pairing, which in the study of religion is called a ditheism or dualism. Dualism was introduced into religious thought by Zoroaster, and continues today in popular Christianity.

However, two also stands for the pairing of God and Goddess, which is known as polarity. A polarity, unlike a dualism, is fertile, and thus this sort of two quickly gives rise to three or even four. However, it might be polite to let these two alone for a while to enjoy one another before we demand that they start having kids, okay?

For that matter, in one sense, it is not two but one that is the first "split from unity", for zero, the Void, can represent a more profound unity even than one.