Nightmare’s Heart
The Grimm Troupe Content
 One realm now must stay apart,  |
The Nightmare's Heart is an NPC in Hollow Knight. It has no dialogue but is mentioned by multiple other NPCs.
Lore
The Nightmare's Heart is a higher being responsible for the Ritual of the Grimm Troupe. It is the deepest power within the Nightmare Realm,[1] and also the one that controls the entirety of the Grimm Troupe.[2]
Grimmchild and Troupe Master Grimm are its spawn.[2] The Ritual performed by the Grimm Troupe is designed to sustain the Nightmare's Heart with a new vessel once the old one dies.[3][4]
In-game events
The Nightmare's Heart is present in the background of the Nightmare King Grimm fight both in Dirtmouth and in 
Godhome. Its eyes glow red when Nightmare King Grimm reaches 50% of his health.
Gallery
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The Nightmare's Heart in Grimm's nightmare
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The Nightmare's Heart in Godhome
References
- ↑ Nightmare King Grimm in
Godhome: "Deepest power... the Heart..."
- ↑ 2.0 2.1 White Lady on the completed Grimmchild: "Success then for the scarlet heart, and irony, to use my spawn to grow its own. I know you creature, and the form time shall bring. You may be all and one, clan and master,"
- ↑ Troupe Master Grimm Dream Nail dialogue: "perfect tool to prolong the heart of Grimm."
- ↑ Grimmkin Master Hunter's Journal entry: "Burn the father, feed the child."