I 1000% believe Gryphon ate the Mythical Gryphon Zoan. Would fit with Cerberus being a dog, and Gryphon being a bird; Shamrock has always been chasing Shanks, his brother who flies free, whereas Cerberus guards the "Hell" of Marijoa (what Sabo referred to is upon seeing the Gorosei and Imu transform).
If Ratatoskr is Ragnir, and Loki is Nidhogg... and Ratatoskr communicates between the Eagle and Nidhogg...
I've said for awhile I believe Shanks IS on Elbaph, but in Heaven World, partying to celebrate Linlin's defeat.
Eagle = Gryphon.
Who has Loki been shown communicating with in Elbaph recently? Which is why Luffy wanted to free Loki?
Shanks.
Shanks' Gryphon is most likely the Eagle at the Top of the World Tree, Ragnir is Ratatoskr, and Loki Nidhogg.
So, I'd expect Ratatoskr to have a good relationship with Shanks, or at least better than Loki does.
If Shanks stopped Loki from attacking Marijoa 6 years ago, to save Loki from a suicide mission, it would make sense for Ragnir to respect Shanks for keeping Loki from throwing his life away to seek revenge.