Slavic Mythology is apparently a difficult field of study as there was no written language before their Christianization. The only written accounts of their religion is from missionaries, who can't be trusted to be completely truthful or objective.
Here is a list of some Slavic mythological figures found at this website
Baba Yaga is a traditional crone goddess - portrayed not as wise and gentle, but frightening and terrible (although sometimes wise as well). She is one of the most frequent characters in Russian fairy tales, where she plays the part of a witch. She lives in a peasant hut made of bones which stands on chicken legs and spins, and is lighted by glowing skulls on posts. She travels through the air in a mortar bowl, pushing it along with the pestle or a broom. She is always very hungry. In mythology, she is sometimes represented as a snake coiled around the Waters of Life and Death.
Byelobog means "white god," and so he appears as an old man with a long white beard, dressed in white and carrying a staff. He is a giver of light, traveling only in the daytime. He leads the lost out of dark forests, bestows wealth and fertility on all, and helps reapers in the fields. He fights with Chernobog every winter and summer solstice.
Chernobog means "black god." He is the opposite force of Byelobog, the lord of darkness, the bringer of calamities and destruction.
Datan is one of three minor Polish gods who guard the fields, along with Lawkapatim and Tawals.
Dazhbog is the sun god, and a kind of chief god, somewhat similar to Zeus or the Dagda. He has horns and a canine head. Dazhbog travels in a chariot across the sky every day like Helios, bringing justice, prosperity and sunshine to the world. He is known as the grandfather of the Russian people. His attendants include two maidens (the morning and evening stars), seven judges (the planets), and seven messengers (the comets). In one myth, he is married to Lada, and the two secure abundance for the world.
Devana is the goddess of the hunt, who roams the Carpathian forests. Her name, as well as her identity, probably came from the Roman Diana.
Dodola is the goddess of clouds and rain. At times of drought, villagers would perform rituals to propitiate her, whcih included pouring water over a flower-bedecked girl.
Dogoda is the god of the gentle west wind.
Erisvorsh is a weather god, though more details are unavailable.
Jarovit (or Gerovit) is the god of war; his name may mean "severe lord." He rules the springtime, looking toward the West. His sacred symbol is his shield, which was kept in his temple and brought out when a victory was needed.
Khors is another sun god, though he is probably of Persian origin.
Kolyada is the name of the god, or more accurately the personification, of winter, and the festival held in his honor. In Ukraine and Belarus, he represented winter while Perun represented summer.
Krukis is a god of blacksmiths and domestic animals.
Kupalo is a fertility god, though like Kolyada he may be more accurately described as the personification of a season, in his case summer. He also known as Kostroma, and his festival is held at Midsummer.
Lada is the goddess of spring, love and beauty. She lives in the Otherworld, called Vyri, until the spring equinox, when she emerges, bringing Spring with her. In one myth, she is married to Dazhbog. Other stories have Lado, a solar god of joy, as her partner and Lel, the god of marriage, as her son.
Marzanna is the personification of death and winter. She is portrayed as an old woman dressed in white. People sought to trick her and thereby prolong their lives.
Mokosh is an earth goddess. She rules over fertility and midwifery. She is commonly called Mati-Syra-Zemlya, or "Moist Mother Earth." Mokosh spins flax and wool at night and shears sheep. She also spins the web of life and death. She wanders during Lent disguised as a woman, visiting houses and doing housework; at night strands of fleece are laid beside the stoves for her. She may have originally been a house spirit concerned with women's work. Evenrually, her worship was transmuted to the modern widespread reverence for Mother Russia. Mokosh is dark, like good, black soil.She is portrayed with uplifted hands, flanked by two horsemen. Mokosh became St. Paraskeva, whose hair hangs long, loosely, and whose icon is decorated with flax and birch. Paraskeva is also known as Mother Friday. One prayer to Mokosh involves going to the fields at dawn in August with jars filled with hemp oil. Turn East and say: "Moist Mother Earth, subdue every evil and unclean being so that he may not cast a spell on us nor do us any harm." Turn West and say: "Moist Mother Earth, engulf the unclean power in your boiling pits, in your burning fires." Turn South and say: "Moist Mother Earth, calm the winds coming from the south and all bad weather. Calm the moving sands and whirlwinds." Turn North and say: "Moist Mother Earth, calm the north winds and the clouds, subdue the snowstorms and the cold." Oil is poured out after each invocation, and finally, the jar is thrown to the ground.
There are many more deities and creatures, unlong with other traditions, listed on the page.
And because I don't feel comfortable posting a blog post that isn't a little bit silly, here's the link to the Wikipedia article about a super villain called The Russian, who first appeared in Marvel Comics in 2000 He also believes Thor would make a good communist because of his big hammer