Crackling Essence is one of the side boss in the The Lord's Labyrinth boss room. Since the layout rotates daily, this monster may or may not present in the layout of that day.
The monster will try to merge with Izaro in its first appearance, which grant the boss a buff that last for whole Labyrinth. In the final boss room, the golem will re-appear and uses its attacks.
It is a lightning golem, a subtype of golem.