There is a certain level of dualism which can be found in Finnish tradition. It's not so much good vs evil, but more similar as can be seen with the yin and yang, for instance.
| Above | Below |
|---|---|
| Life | Death |
| South | North |
| East | West |
| White, bright | Black, dark |
| Warm | Cold |
| Trees with leaves | Trees with needles |
| The self | The other |
| Dressed | Naked |
| Clockwise | Counter clockwise |
| Right hand | Left hand |
| Right side out | Inside out |
| Waxing moon | Waning moon |
| Male? | Female? |
When it comes to male and female division, there is some evidence but it's not certain. Another thing, it is not good to conceive a child during a waning moon as it's connected to the "death side". While this "death side" represents the Underworld, the "life side" represents both this world and the heavens. I guess there was no point in differentiating between them as Finns were not super interested in the heavens: leaf trees are good for worship of both deities on this layer as well as the ones above.
Many researchers have concluded that the original Uralic creation myth was quite different from what the Finnish creation myth eventually became. In the original version, it would've been a waterfowl which brought soil up from the bottom of the primordial sea and from this, land formed. At some point, the myth got more dualistic features. This can be seen in the Komi creation myth even today, in which the creator god Jen took the form of a swan to bring up an egg from the bottom of the sea to create the world. However, his brother Omöl, taking the form of a grebe, also participated, being the originator of the evil things and imperfections of the world, becoming the Underworld god. This dualism still exist in Finnish myth as well, even though it is a bit hidden. In Finnish tradition, the Underworld deity was turned into a woman, Louhi. However, her celestial counterpart is also not the sky god, an equivalent of Jen, but the sun goddess Päivätär (who could be related to the Proto-Uralic sun goddess, wife of the sky god?). While the two are not connected to the creation myth anymore, the dualism between them still effects the cycles of life and death.
The above tablet of dualism is based on Actual Research TM. This below one is based on my own musings only!:
| Life | Death |
|---|---|
| Päivätär | Louhi |
| Päivölä | Pohjola |
| Lemminkäinen | Son Pohjolainen |