Insomnium have put out "The Hour Grows Late" on the day Netherworlds itself arrived, and the guest list is the whole of the other band: Tomi Joutsen, Tomi Koivusaari and Santeri Kallio of Amorphis are all on it.
Those two bands have circled each other for twenty years without doing this. One guest is a favour and three is a decision, and putting a singer, a guitarist and a keyboard player from the same band on one song means the arrangement was written to hold them rather than to display them.
Jari Heino directed the film. Releasing it on the day of the album rather than three weeks before is also deliberate: the song is not bait for the record, it is a reason to go back into it once you have heard the whole thing.
Finnish melodic death metal has been a small world with the same names in it since the nineties, and this is what that looks like when it works in favour of the music instead of against it.