Allright, the first part. Slavic paganism.
Written sources about our ancestors worldview are scarce, but Rus' was baptised relatively later than most of other european countries, so many of paganistic elements are still alive in our traditions.
Judging what sources we have, it was some kind of pantheistic religion, and a pantheistic element was so strong, that were included in early forms of ortodoxal Christianity.
http://www.litra.ru/fullwork/get/woid/00345821231862344106/"Our free white light was coceived from the Lord's judgement,
(Red/Beautifull) sun - from Lord's face,
The Christ himself, the Zar' of (Sky/Heavens);
Young bright moon - from His chest,
Rife stars - from Lord's vestments,
Dark nights - from Lord's thoughts,
Morning dawn - from Lord's eyes,
Rough winds - from The Holy Spirit,
Rife rain - from Lord's tears,
The Christ himself, the Zar' of (Sky/Heavens);
We got a mind of Christ himself,
Our thoughts are (concieved) from heavenly clouds,
Our (world/peace/society) is from Adam,
Our strong bones are from stone,
Our bodies are from damp (soil/land/Earth),
Our ore-like blood is from black sea.
That's the source of Zar's in our land -
A holy head of Adam,
A holy (relics/corpse) of Adam.
That's the source of ortodoxal (christians/paisants) -
A holy knee(?) of Adam"
Second interesting thing. Though being trinary - just like Scandinavian - slavic world was also binary. The trinary division includes Upper world - Eerey, our world (name lost) and lower world (name lost). The binary division includes our world (presumably called Yav') and the world of dead - Nav'. In modern slavic neopaganisn this led to a single trinary division on Prav' (upper world, Asgardr), Yav' (our world, Midgardr) and Nav' (lower world, Hell).
While it's unclear what divides the Upper World from the others, it's known, that Yav' and Nav' are divided by a big water - an ocean or a river. And as it's unlikely that our ancestors have any chance to see an ocean often enough, it's most likely a river.
The Smorodina river. "Smorodina" can be translated as "currant" - the modern meaning of the word, or "stinky" - the old meaning. You can easily reffer to this river as Lethe. The Smorodina river plays a role of a border between Yav' and Nav'. A border, that can be traversed via the Kalinov bridge. This name is also polysemantic: it can be a "Guelder-rose bridge" or a "Red-hot bridge" (the Bifrost if you like). The Kalinov bridge is a big element of slavic mythology, as it often appears to be a place for an epic battle between light and dark.
The way through Kalinov bridge is oftenly guarded by Zmey (Wyrm/Serpent/Dragon) Gorynych (Griefson/Mountainson/Burnson). More about him later.
Our ancestors believed, that the base of a known world is an island, called Booyan (therefore everything separated from it by a big water and/or a big distance is percieved as Nav' - foreign land=afterworld, long-term expedition=death, coming back=resurrection). Booyan is heald by the Keet (Cete, Leviathan and a modern Russian word for Whale); or the Indric, basicaly - a unicorn. Whoever holds the island, he got's tired, and Booyan is allready 3/4 drowned.
Percieving Nav' as a distant land and/or a big water also found it's place in slavic neopaganism, specifically - in a so called "The Left Hand's Way". More of it later.
Now the gods.
Peroon (aka Perkunas, Pyarkunas). Every european culture have it's own thunder god, in Russia it's Peroon. He's a thunder god, a warrior god, his main job is to ride-around in his chariot and zap any nasty thing he sees. His main opponent is the Zmey (mb Gorynych, but it's uncertain). In later tradition Peroon is associated with st.Elijah.
Veles (aka Volos). Trickster. A god of cattle, wealth, shakes and underworld. Could be a nemesis of Peroon, or his ally - it's, again, uncertain. In later tradition Veles is associated with st.Blaise of Sebaste and/or st.Nicolas. In some versions of slavic neopaganism he is a brother or a husband of Mara.
Svarog - god of smithery, fire, fatum and oaths. Densly associated with Peroon. In some sources presented as a ruler of SUDDENLY Egypt. In later tradition Svarog is associated with st.Cosmas and st.Damian.
Dazhd'bog (aka Dabog) - son of Svarog, solar god, progenitor of slavic nobility or even all the slavs. Southern slavs have a legend about the Zar' Dabog, overthrown by The Four Letters.
Khors - little is known about him. Thunder god (mb), solar or munar god.
Streebog - the god of wind.
Magozh (aka Makosh, Mokosh). Wife of Svarog, the godess of fate, motherhood and husbandry. Associated with very ancient Mother-Damp-(soil/land/Earth). In later tradition Magozh is associated with st.Mary. Her main attribute is a spinning well, her sacral bird is a swan - an images of Swan Princess and Vasilisa the Wise are most likely came from Magozh.
Zheeva (aka Crasopani, Jijilelya, Sieva, Ziza). Godess of life, fertility and sex. Her attributes are roses, lilies, and a golden bird-drawn chariot. Possible avatara of Magozh.
Lada. Russian automobile concern and one more possible name or avatara of Magozh.
Mara (aka Morana, Morena, Morzhana, Morgan). Hel. Nuff said. Godess of death, winter and underworld, could even play a role of a Grim Reaper. Legend says, that those affraid of dying will see her as an ugly and grumpy old lady, but those who are brave and calm in the face of death will see Mara as a young and beautifull gothic brunette.
A few words about the Left Hand's Way. The LHW is a gnostic branch of slavic neopaganism that sees Mara as a liberator from the tenets of existance, the nemesis of Svarog. In LHW besides Prav', Yav' and Nav' there's also The Great Nav' - the initial black abyss of a perfect nothing, a raw nonexistance, a dark, grim, gothic Nirvana - a home for Mara and a place she's willing to return everyone to by the means of a total discreation.
Semargle could be just a lingustic misstake or a slavic Mercury - the heavenly courier in a form of a winged dog.
Yareelo (aka Yarovit). Solar god, that was discovered only at 1765-th. Could be a classical dying-god figure and/or a "slay-the-dragon-save-the-princess" type.
Rod (aka Sood, K'rt). Little known deity, noone knows for sure, was it even a thing. But there's a version, that Rod was The Boss, and thus his name was held taboo - and that's why we know so little about him. Many of neopaganists are agreed with this version.
The White God and
The Black God - demiurges, according to some legends.
Svyatovit (aka Svetovit, Svantevit, Sventovit) - four-faced deity of polab slavs. The god of wisdom, the guardian.
TBC.