Vi'el is a level 60 exotic reagent vendor located in a small cave just inside Darkwhisper Gorge in the contested territory of Winterspring. The cave entrance is guarded by lvl 60 elite Hederine mobs.
He sells the [Fel Elemental Rod], which is required for the quest [60] A Shifty Merchant (Elite). He also sells a limited supply of 5 Gromsblood, which is on a timer and may take 45 minutes or longer to reappear.
See List of Winterspring NPCs.