During the week of October 11, 2016 this card was available in a weekly card pack, along with Guardian's Key and Fountain Spike. You can still earn the contents of that pack through weekly quests.
Dreadfeast Relic, in addition to 4%Crit Chance and 5%Lifesteal also has an Unique Active which, for 6 seconds, on hit with any of your abilities, applies 12.5% Life Grant to targets for 4 seconds. Attacking an enemy marked with Life Grant gives 12.5% Lifesteal to attacker.
Lifesteal from Life Grant stacks with other sources of Lifesteal.