The set is Witchman, it has nearly the same effects as the passive Battle Roar from Dragonknight, restoring attributes based on ultimate cost... can they stack?
Witchman Set info: "(5 items) When you use an Ultimate ability, you heal for 31 Health and you restore 28 Stamina per point of the Ultimate's cost.";
Battle Roar info: "When you cast an Ultimate ability, you restore 30 Health, Magicka 33 and 44 Stamina for each point of the Ultimate's cost.".
Example: "Magma Shell: On cast it will restore 12200 health, 14400 (+5% based on missing stamina) and 6600 Magicka." It's a very good heal combined with the ultimate's own benefits.
Glory for the Pact!