I am familiar with these artifacts. I believe that they were brought here by Magatha Grimtotem herself. But she's not amongst the Grimtotem on Darkcloud Pinnacle. She disappeared right after she arrived, and no one knows where she is now.
Maybe we can find out.
Take the rattle, the writ, and the drum out to Arikara's Needle. If my guess is correct, the wind serpent will appear again. You'll have to defeat it to gain knowledge of where Magatha is hiding.
Exit the cave, cross the bridge, take a left. At [38.1, 35.3]
in the center of Arikara's Needle, use the artifacts. She is a level 43 elite wind serpent with 10984 health. Her primary ability is Lightning Bolt, which hits for ~140 Nature. Every 20% or so, a Grimtotem Spirit will spawn, applying Ancestral Fortitude to Arikara, shielding it for 100% of damage taken. Kill it to drop the shield, then keep working Arikara down.
Aggro:
Arikara yells: Thank you for the gifts. Let us see if you are worthy, <class>!
First shield:
Feralas Sentinel says: The creature is gaining power from the ancestral Grimtotem! We must put them to rest if we are to defeat the beast!
Victory:
Arikara yells: Stop! You have bested my wind serpent.