There are (but very few) song texts speaking about devil, hell and souls, thus showing direct influence of the Christianity. Much more can be found in the folk-tales, but they are also dominated by international motifs. To sum them up: the Devil is living in a different world, possessing wealth and magic powers, which can be earned or taken by wit or force; the Devil tends to kidnap people (mostly young maidens); and Ragana ("witch") may be his wife.
Again many of the traits seem to be coming from Christianity. There are some motifs when the devil is honest and helping the weak and poor; maybe this is some form of syncretism as the evil force takes those who have been evil. The devil may at the same time represent some old pre-Christian deity, banned, with changed semantics, but still with something left of the ancient, good "archetype". There is also a group of folk-tales on the stupid devil, to some extent similar to the Nordic trolls. This devil is living somewhere in lakes or fens, is physically strong and rich, but a small shepherd-boy can simply outwit him.
A special motif can be that of Velns' name. In folk-tales and folksongs there are cases when knowing the name gives some power over the Devil himself or other things in the world, but sometimes it is just a means of protection. The word used to designate the Latvian devil may be related to that of Velis, i.e. the inhabitant of the otherworld.
Velna mate is also one of the images in the ritual songs. She is the woman who is killed by the hero, which causes the hero's impurity - he has to wash off her blood, which is not easy. This motif is quite independent and can be found in several different myths of Latvian folksongs.
There is a parallel to Velns: Jods. Taking into account the meaning of juodas in Lithuanian - "black" - it does not add much to the understanding of this personage, which corresponds with the usual description of the devil. Velna mate is also paralleled with the Joda mate.
Therefore, to summarize, it can be said that there could have been no division between the good in the form of God and the evil in the form of Devil in the ancient Latvian mythology, as even Laima may be good or evil towards a particular person. Formation of this image has definitely been influenced by the Christianity. At the same time the image has included the notion of hostile minor deities, those of the underworld or any other unexplored and mysterious place treated as such in mythology. In the whole, this image could be of more recent origin.