Bloodthorn’s Touch is a light armor set. When you deal direct damage, you restore 660 Magicka and Stamina. This effect can occur once every 5 seconds.
Bloodthorn is a very popular set in PvP because it can be placed on one bar only. A lot of players run this set on the backbar to activate the recovery effect when they weapon swap every 5 seconds. This allows players to slot something else on the frontbar. Now for some math: 660 divided by 2.5 is 264. Which means this set equals 264 Magicka Recovery and Stamina Recovery when you would place this on the Character stats sheet. This cannot be increased with other modifiers. Normally when you are blocking your Stamina recovery equals 0; however, with this set you will still get Stamina back from the unique 5-piece set bonus.
Tanks also use the Bloodthorn's Touch set in some PvE builds, even though it drops in light armor only. They normally only wear the jewelry items, weapons and shields of this set to achieve the 5-piece bonus, and combine it with a full heavy armor build (a 5-piece heavy armor set on the body pieces, plus 2 heavy armor Monster set pieces).
The Bloodthorn’s Touch set is part of the base game. It drops in Glenumbra in the Overland content. You can also find it on Guild Traders. Each set item is bound on equip. You can acquire light armor, jewelry and weapons for this set in the Primal motif style.