Hi, I have tried to do it on my own, but first of all it is really exhausting to create a lyrics for a language you don't speak and second of all, the sound quality of the video makes it hard to hear the specific sounds of the song.
The link of the actual song: https://www.youtube.com/watch?v=3Y7aQvbA1fM&t=6s
Lyrics I have derived (or at least tried to) to-date (dubious lyrics in Italics):
Hoyr nú har sum kemur her
Tað besta trøll hvør hevur vert
Í Mumidalinum han býr
Hann elskar spæl og ævintýr
Nú kemur Mumi
Nú kemur Mumi
Við vinum sínum hann mein ber
???
???
???
Nú kemur Mumi
Nú kemur Mumi
If you could help me, I'd be very grateful.