Essence

There are two types of  but what they both have in common is that it is dropped by enemies when killed.

Stimpack essence
This type of essence is used to craft stimpacks.
 * Damage Essence
 * Invisible Essence
 * Life Essence
 * Speed Essence

Elemental essence
Elemental essence is used to craft elemental weapons and armors.

Which essence you get depends on what element the enemy belongs to. You recieve Essence of Fire for killing fire enemies, Essence of Ice for ice enemies, and so on.
 * Essence of Electricity
 * Essence of Fire
 * Essence of Ice
 * Essence of Moonlight
 * Essence of Poison
 * Essence of Soul

Elemental Prefixes
The easiest way to tell what element the enemy belongs to is to look at the prefix in their name and their color.

Normal: Tough, Brutish, Thuggish, Intimidating.

Fire: Combusting, Scorching, Blazing, Inferno.

Ice: Frozen, Icey, Frigid, Arctic.

Electric: Sparking, Shocking, Lightning, GigaWatt

Poison: Infected, Toxic, Miasmatic, Baneful.

Moonlight: Luminous, Dazzling, Brilliant, Blinding