Sacks or cocoons used for the metamorphosis of land dreugh to sea dreugh (called Meff in lore) or vice-versa (Karvinasim). Possibly the lore name for the sacks themselves is Grom, although it's not clear whether that's TES III lore or not.

It is up to the claimant whether to make two separate types of cocoons for these transformations. Easier would be just one type for the both of them.

I made an orange-tinted version of the vanilla mist assets to add a bit of depth to AT's visuals. I still haven't tested them in-game, and may still adjust them to get the best (hopefully) effect.