Ferocity is an 
Vitality Gem. This Offense type Gem can be slotted in the fourth slot of the Vitality attribute tree for a total 19,000 
Gold cost.
Slots 1/2/3/4/5 are at nodes 1, 7, 13, 19, 25 respectively
How to obtain[]
Ferocity can currently be earned only through chests. Higher rarities have a lower chance of dropping.