Are Ethwahl and Death's Dance darkin?
Etwahl seems to have a symbiosis with sona similar to darkins having symbiosis with their host. According to sona's old lore, her care takers tried to sell the instrument but it kept returning as if it had some sentience and sona specifically could use its power. Granted it doesn't really look darkin but is that a requirement? Also the name doesn't have an "aa" emphasis which may or may not be a darkin characteristic.
Also
This just flat out looks darkin, and unless the blade itself is call "death's dance" the demon or whatever the blade is doesn't have a true name.

, since the lore mentions that is a living being.
Pretty sure Sona has nothing to do with the darkin, for the item deaths dance it would be a waste to have it just as an item instead of a champion