I made this Fjarnskaggl farming guide to help out players who want to farm the herbs instead of buying them from the Auction House. You can pick this Herb from skill 1, you will get the same number of herbs as if you had Herbalism 800.
One of the new features in World of Warcraft Legion is that herbs have ranks now. You can get the new ranks from quest items that you get from picking [Fjarnskaggl]. Once you finish the quest you get from the herb and the follow up quest, you will get the new rank.
Rank 1 : Gather Fjarnskaggl more effectively.
Rank 2 : You can get [Blood of Sargeras] when gathering Fjarnskaggl.
Rank 3 : Mount quickly after gathering any herb in the Broken Isles.

Fjarnskaggl

Get these three items to speed up farming: [Leystone Hoofplates], [Demonsteel Stirrups], [Stonehide Leather Barding].
You should also enchant your gloves with [Legion Herbalism].
StormheimFjarnskaggl can only be found in Stormheim. Every other herb in the Broken Isle have a chance to spawn a creature that gives you more herbs, but it seems Fjarnskaggl doesn't spawn anything.