Spirits

Ghosts are the remains of a deceased bug given visible form. They are only visible in-game after acquiring the Dream Nail. Ghosts can be consumed by hitting them with the Dream Nail to acquire only 1 Essence; however, this does not count towards completion and the Essence is not necessary to fully awaken the Dream Nail.

Trivia
 * Ghosts were a reward tier in Team Cherry's Kickstarter campaign for AU$ 150:
 * "Ancient Wanderer: Appear in-game as a bug spirit in the Glade of Hope! Help create the appearance and dialogue for your spirit counterpart: Tell of a previous life, aid the Hollow Knight on his quest, or taunt him as he passes by."


 * It is unknown exactly what ghosts are in Hallownest. Some of them do not seem to have knowledge of the passage of time or even their own deaths, nor are they able to move from where their corpses presumably are. Considering they give Essence, which is made of dreams, it could be that they are simply imprints of the deceased bug's memories, rather than the actual spirit or consciousness of said bug.
 * The ghost of Cloth does seem to be aware of her death as her ultimate goal was to reunite with Nola, who is presumably deceased.
 * If the Defender's Crest Charm is worn while in Poggy Thorax's secret room, a large number of hungry flies swarm around the Knight.
 * If Cloth's side quest has been followed, she shows up in the Queen's Gardens to help in the fight against Traitor Lord. The fight ends with Cloth and the Lord's demise, and Cloth's ghost can be seen and spoken to upon leaving and re-entering the room where the fight took place.

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