|“||Through dream I travel, at lantern's call, to consume the flames of a kingdom's fall.||„|
|~ Grimm's riddle in the Hunter's Journal.|
|“||Masterful! Even a vessel discarded bears fierce strength. Fine craft dear Wyrm, and perfect tool to prolong the heart of Grimm.||„|
|~ Grimm's thoughts on The Knight after the player defeats him for the first time.|
Grimm, also known as the Nightmare King, is a supporting antagonist in Hollow Knight, introduced in "The Grimm Troupe" DLC. He is the villainous leader of the mysterious Grimm Troupe, a group of performers who seek to collect the flames of the fallen kingdom of Hallownest in order to prolong the Nightmare's Heart, a process the Troupe calls "The Ritual", and manipulates the Knight into doing his bidding.
Grimm first appears when the Troupe is summoned to Hallownest by the Knight lighting the Nightmare Lantern in a hidden area in the Howling Cliffs, after which they set up camp in Dirtmouth. Inside the main tent is Grimm, who greets the Knight and explains that the Grimmkin now travel across Hallownest to collect the "flame in dream". He gives the Knight the Grimmchild charm, and encourages them to seek and defeat the three Grimmkin who have gathered flames in order to upgrade the Grimmchild.
After defeating the three Grimmkin and collecting their flames, Grimm appears when the Knight and the Grimmchild return to his tent and uses the flames to upgrade Grimmchild into a deadly companion. He then sends the Knight out to find three more flames to further grow the Grimmchild so he can begin the performance. Following the next three flames, Grimm leads the Grimmchild into his body and challenges the Knight in a duel. After defeat, Grimm congrats the Knight and mentions how they have potential in prolonging the Nightmare Heart. He awards them with a charm notch and returns the Grimmchild, now at its third form, and encourages the Knight to seek out the last three flames so the Ritual could begin.
Following Grimm's boss fight, the player is given two options to complete Grimm's quest: first is to collect the remaining three flames and return to Grimm, who now sleeps in the back room of his tent. Dream Nailing him takes the Knight to Grimm's dream in the nightmare realm, where they must fight against Nightmare King Grimm to complete the performance and finish the Ritual. Defeating him there will transfer the Nightmare's Heart from Grimm to the Grimmchild, granting the Knight the fourth and final form of the Grimmchild. Defeating Grimm causes the Grimm Troupe to vanish, although Divine will stay behind and upgrade the fragile charms.
However, talking with Brumm in the Deepnest before collecting all three flames and following him to Howling Cliffs to quench the flame of the Nightmare Lantern will cancel the Ritual and banish the Troupe. The Nightmare Lantern is the anchor through which the Grimm Troupe can manifest in the waking world, and destroying this anchor banishes the Troupe back to the nightmare realm.
In his regular appearance, Grimm is a slender dark being covered by a multicolored cloak, with a gray exterior and a red interior. His face is pale with red eyes, and underneath his cloak, his body is scaled and purple. As the Nightmare King, Grimm's body turns entirely red, with his cloak having a maroon color. His face remains pale and his limbs remain black.
Grimm, throughout all of his interactions with the Knight, remains polite and respectful, bowing in shows of respect to them on several occasions. He is dedicated to the part he plays in the Ritual, and has a flair for theatrics, keeping with his persona of the leader of a traveling troupe. He views battle as a form of dancing and in combat shall unleash moves that cause his always nearby audience to cheer.
His respect extends to the Godseeker, for when summoned to do battle with the Knight before her, he shall again bow towards her. Dreamnailing him shows Grimm is in fact delighted to be in Godhome, viewing it a pleasure to take part in the Seekers quest to find the strongest creature in Hallownest.
- Grimm (particularly his Nightmare King form) is based on vampires, most notably Dracula.
- At the beginning of the battle, if Grimm is attacked while he is bowing, he lets out a banshee-like screech and retaliates with his Flame Spawner attack, which he normally only uses when his health reaches 75%, 50%, or 25%.
- The Grimmchild charm is required for both battles. The Grimmchild itself, however, cannot participate in any of Grimm's battles, even if equipped in Godhome.
- The audience in the background applauds every time Grimm uses his Fire Spawner attack and reforms after being staggered.
- At the beginning of the fight, Grimm will always bow towards the Knight unless he is fought in Godhome, where he will bow towards the Godseeker audience instead. Regardless, attacking him whilst bowing will cause him to screech like in his fight outside of Godhome.
- Grimm's health is determined by the Knight's Nail upgrades, gradually increasing depending on the upgrade level. This also applies to the Grimmkin, the Dream Warriors, Dung Defender, and Hive Knight.
- Nightmare King Grimm is tied with the White Defender as having the second-highest health of any boss in the game, only behind The Radiance.
- Along with the Radiance, Nightmare King Grimm has a full-screen title card. It isn't uncommon for fans to speculate that he is related to the Radiance in some shape or form. Some fan-works even depict him knowing the Radiance personally.
- While uncertain what species Grimm is given all characters in the game are bugs, the most accepted theory is that Grimm is a moth, particularly a Calyptra, or the vampire moth.
- Grimm is a popular subject of memes, jokes and trends amongst the Hollow Knight meme community due to his character.
- One of the most common jokes relating to him is that the fandom nicknames his flamespawner attack as the "Pufferfish Maneuver".
- YouTubers who bow to Grimm in their lets-plays are met with praise for respecting Grimm's bow instead of interrupting him.
- His head-shape has led a few fans to compare him to Bendy hence his resemblance.
- As of now, Grimm's battle theme is the only song in the Hollow Knight soundtrack to feature an electric guitar.
- Grimm's theme is one of the most famous and remixed pieces from the Hollow Knight soundtrack, with it usually being the first song remixed by a music YouTuber from the game. Currently, Retrospecter's medley of Grimm's theme and his theme as the Nightmare King has over one million views.
- Nightmare King Grimm will almost always begin the fight with his uppercut attack unless he scurries away from the Knight after teleporting too close to them.
- Grimm is the only higher being, other than the Radiance, to actually be fought in-game.
- Since Grimm travels to other kingdoms to collect Nightmare essence, he may make an appearance in the upcoming game: Hollow Knight: Silksong. Even though it is set in another kingdom.
Hollow Knight: Silksong