It's an herb in shadowmoon valley.

what herb skill do you need for this?

your nature resistance will affect the amount of damage you take from picking these.

I don't take any damage at all from collecting these. There is an animation that would look like something hitting my character but i don't get any debuff or take any damage. I only got 10 nature resistance atm so it can't be because of that.

Geez, it's no where to be found. I've found maybe 3 nodes since I became 70, a week after TBC came out. If you think Mana Thistle and Netherbloom are rare... You're going to need some prozac to get through looking for this stuff alive. I can tell you that it's not like Mountain Silversage, it can grow on flat ground. Also, I've seen it by the undead Arakkoa camps... Hope this helps =/

When picking this herb, you have a chance of looting Fel Lotus. Out of the 42 nightmare vines I have in my inventory, I got 2 Fel Lotus.  I received my first Fel Lotus off the first nightmare vine I harvested.

The debuff is a poison. Can be dispelled by Druids Abolish Poison, and other poison dispels as well I guess.

I've found a reliable spawn for this at the southern tip of Quel'Danas Island, right at the beginning of the Dead Scar.

where is a good place to farm these ? i can never find them.

Lhara sells these for 50s every darkmoon faire.  it's limited and respawn time is a bit long.