Where does Hex Siphon item-set drop in ESO?

Hex Siphon item-set can be *found* in Vateshran Hollows.

What type of set-item is Hex Siphon?

Hex Siphon is a(n) Arenas item-set.

Hex Siphon (ESO Sets) - GuildPlanner.Pro

Means to Obtain

Vateshran Hollows

Bonuses

(2 items) Adds 1032 Maximum Magicka
(3 items) Adds 121 Weapon and Spell Damage
(4 items) Adds 618 Critical Chance
(5 items) Adds 161 Weapon and Spell Damage
(5 items) Whenever you Bash an enemy, you release a cone of hexing energy in front of you. Each enemy hit increases your Weapon and Spell Damage by 83 for 8 seconds, up to a maximum of 6 enemies. This effect can occur once every 8 seconds.