Reactive Spells is an 
Intellect Gem. This Utility type Gem can be slotted in the fourth slot of the Intellect 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[]
Reactive Spells can currently be earned only through chests. Higher rarities have a lower chance of dropping.