Valkyrie is inhabited by three broad groups, known as land-dwellers, sea-dwellers, and sky-dwellers. These are then split up into individual species, of which there are many thanks to the overflowing life force of Valkyrie.
Land-dwellers
Land-dwellers, common name skogsrå, are those that cannot live in the water, nor traverse the sky, but can live on the water and on dry land.
Slimefolk
On Valkyrie, slimes are not uncommon, often the result of raw magic associating itself with a physical object. Due to the way the magic system in Valkyrie works, slimes can easily overpower an unprepared organic being; slimefolk are the result of this.
They are commonly considered land-dwellers, but can inhabit semiaquatic environments like the Glistering Caverns. It's also believed that these are the source of the slimes "Final Angel"'s world Chroma City.
Fiends
Fiends are considered land-dwellers, but inhabit the space between realms, and also appear in National Mana League. Powerful ones can rend space, transporting themselves or objects near-instantly. Some hypothesize that rather than their home turf being between realms, it is somewhere beyond the seas surrounding Valkyrie, but if this is true, they do not say so.
Poltergeists
Poltergeists are a species of non-organic lifeform - usually, a spirit - that has become associated with an object. These can be made naturally or artificially. Generally, a poltergeist has an anthromorphic "presentation." However, these are not different "species" of poltergeist, as the presentation is not the spirit's true body (this is the object they are associated with) and the spirit themselves chooses their appearance.
Sea-dwellers
Sea-dwellers, common name sjörå, inhabit the oceans and aquifers of Valkyrie. Notably, there is a huge aquifer, known as the Glistering Caverns, with a large sjörå population.
Sky-dwellers
Sky-dwellers, common name bergsrå, are similar to land-dwellers in that they require air, but unlike them, they can naturally traverse the sky. Their common name comes from their association with mountains, natural high places, but they often inhabit highlands all over Valkyrie.