Essential



Essential is an attribute which can be assigned to non-player characters where the character cannot be killed, instead, will be temporarily rendered unconscious, returning to normal after a short period of time. The equivalent attribute for items is quest item, which should not be confused with the general usage of the term.

Gameplay
This attribute is used in games which use the Gamebryo engine, such as Fallout 3 and Fallout: New Vegas, or the Creation Engine, encompassing both Fallout 4 and Fallout 76.

The main purpose of this attribute is to protect the integrity of certain quests which do not account for the death of an NPC important to its progression and plot. This prevents the player character from breaking the quest and making it impossible to complete by killing an important NPC. However, there are still characters involved in quests that can be killed, but most of the time their deaths will result in the quest being failed or proceeding differently.

The completion of certain quests or tasks will make the NPCs associated with them able to be killed, though most characters integral to the main plot of their respective game are marked as essential permanently throughout gameplay. Sometimes the death of an NPC associated with a quest will result in a pop-up message informing the NPC in question has died, with the quest subsequently failing.

Ghost
"Ghost" is an attribute which can be assigned to non-player characters, resulting in their immunity to all damage. Any attempts to strike them will not result in hit effects nor will it trigger hit events. Unlike the essential attribute, the ghost attribute causes the character to actively ignore all forms of attack.

Children and companions
All children are marked essential, but they differ from other NPCs marked with the attribute in the fact that they are also coded to not take damage from any source, thus cannot be killed or knocked unconscious. Children can be still attacked, but they will always cower and flee instead of retaliating against the player character, and cannot be targeted in VATS.

In Fallout: New Vegas, the only NPCs aside from children that are essential during gameplay are companions currently in the player character's party. However, companions are not marked as essential if one is playing in Hardcore mode.