#sonneve

Some years ago, Ross Downing put together a book of heathen prayers compiling everything he could find from pre-modern sources. His website has been down for a while and I can't seem to find a way to access the book as a PDF, but there's a reel of maybe the whole thing on his instagram. I think it's a stretch to call some of what's included "prayer" (and he fudges some translation like on the Sparlösa runestone) but that does still seem to fit your criteria.

Interesting article by John Lindow about prayers to Thor (generally in the form of recounting times when he kicked ass): https://www.jstor.org/stable/40918940

I think some of Freyja's opening stanzas in Hyndluljóð are arguably prayers or at least prayer-like, as well as the final line of the poem: Bið ek Óttari öll goð duga 'I ask that all the gods aid Óttarr' (biðja is actually also the word used for 'pray' though in other contexts it just means 'ask' or 'request').

I don't know if this is the sort of thing you're looking for but there are examples of poems and formulae in later folklore that you might be able to frame as prayers depending on how you define it, though they were not likely conceived as such in their own time. An example that comes to mind is Galdra-Brandur's invocation of Gylfi (here, presumably a being related to cold like a hrímþurs, rather than a human king) to wipe out swarms of biting flies:

Gylfi hæða galhvassan gefi vind á landnorðan með óveðri magnaðan mývarginn svo drepi hann.

(roughly) 'May Gylfi give harsh highland wind in the north with magnified storm-weather so may he kill the mývargar (biting flies).'

But that's way later than Old Norse times and not a reliable witness to a person actually speaking (Galdra-Brandur was a real guy but known mostly through tall tales).

Festivals, it's primarily Winter Nights and Sigrblót, along with my own created ones such as Ránarblót and Eirarblót — Ránarblót has significance for me on a local level, and Eirarblót has personal meaning because that falls on the anniversary of when I started my proverbial fight against testicular cancer. On the Brittonic side of my practice, there's Brigantica/Iwos Brigantia, Boudiwaris (another one of my own making to mark the coming of spring), and Litus Maponi (one I created with Drunertos of Albionandbeyond.com).

What brought me to my practice? I'd always been fascinated by the Norse myths since I was a kid, as well as the history of the Viking Age. I dabbled in Wicca and Witchcraft when I was about 18 for a brief period, then sort of strayed off the path a bit, so to speak, and ended up being a Mormon for a brief stint (I was in a dark place at the time). Once I realised Mormonism wasn't for me and there were things that other members said that made me uncomfortable, I started looking back into paganism and landed on Heathenry. A few years back, I started exploring Brittonic Polytheism as well, due to what I interpretated to be a sign from Brigantia during in a period where I was in what essentially became a legal battle with my former employer.

I mostly know Icelandic folklore, and there isn't a whole lot about fiddles there. I don't know if there's anything there about hardangers in particular, and fiddles in general weren't very common in Iceland; a few were imported in the 19th century and it's said that a handful of Icelanders were able to make their own, and it supposedly had a reputation for attracting huldufólk.

I'm not sure what languages you're able to read, or your tolerance for retyping things into Google translate. If you're sticking with English, the book Scandinavian Folk Belief and Legend, edited by Reimund Kvideland and Henning K. Sehmsdorf, has a bunch of stories about fiddles and water spirits (nøkk/näck, fossegrim), and then a little bit about fiddles and the devil, all with citations. It's not hard to find a PDF of this book.

54.14 "They Danced themselves to Death":

Finally a minister heard about the dancing on the mountain, and when he commanded the fiddler to stop, the man had to obey. But the folks who had followed the minister saw that it was Old Nick himself who sat there and played. He used his ass as a fiddle and worked it with the bow.

If you're able to read Scandinavian, the book -og fela ho lét. Norsk spelemannstradisjon by Arne Bjørndal and Brynjulf Alver is cited frequently by the above. It's available to borrow one hour at a time on archive.org. Studier i svensk folklore by Tobias Norlind is also available online, and the second volume of the Atlas of Swedish Folk Culture is available to download here.

Animal spirits aren't really part of my practice at the moment. That might change in the future though, but for the most part, I occasionally light a candle for my cats who have unfortunately passed on, especially Biscuit, since he was the best of them