Grimm in Hollow Knight is a character that is presented as both an NPC and boss.

After you assist them in this task and complete The Grimm Troupe quest, Master Grimm will be available as a companion to the Knight in the form of Grimmchild. The Grimmkin are ghostly wisp beings of flame who serve Grimm loyally. The Grimm Troupe gathers scarlet Flames, remnants from dying kingdoms with the help of Grimmkin. Although intimidating and perhaps sinister-looking, they do not appear to be harming anyone as they feed on the residual energy of dead kingdoms. To perform this task, the Troupe deploys ghostly beings of flame called the Grimmkin. The goal of the ritual is for the current Troupe Master Grimm to be reborn by fire, becoming the Grimmchild (who will in time mature into Troupe Master Grimm once more to continue the cycle). They travel to wherever their scarlet Lantern has been lit, gathering scarlet flames from the ruins of kingdoms long gone. Grimm in Hollow Knight is the leader of the mysterious ghostly Grimm Troupe. Troupe Master Grimm is also the main character for The Grimm Troupe (Quest). Upon entering his nightmare, you will encounter his Dream form, the Nightmare King Grimm. Speaking to Nymm grants the Carefree Melody Charm, which takes up the same slot in the inventory as Grimmchild.Troupe Master Grimm is both a Boss and an NPC in Hollow Knight. Returning to Dirtmouth reveals the presence of a new NPC, Nymm, while the entire Troupe is nowhere to be found. Doing so removes the Grimmchild Charm from the inventory and grants the Banishment achievement. If instead Brumm is approached at the Howling Cliffs, the Knight can help him destroy the Nightmare Lantern and banish the Troupe. The Grimmchild is upgraded one final time, and the Troupe leaves Hallownest, with the exception of Divine, who stays behind until all Fragile Charms ( Heart, Greed, and Strength) are made Unbreakable. Defeating the Nightmare King completes the Ritual in Hallownest, granting the Ritual achievement. Returning to Grimm's tent with three flames collected and Dream Nailing the sleeping Grimm initiates the Nightmare King Grimm boss fight. He then tells the Knight that if they so wish, they should meet him where it all began. When listened to, Brumm will suggest breaking the cycle of the Ritual and banishing the Troupe from Hallownest. One of those four flames is carried by Brumm in Deepnest. The final phase of the Ritual has not three but four flames scattered around Hallownest. Defeating Grimm upgrades the Grimmchild once again, grant the Grand Performance achievement, and a Charm Notch, and allows the Knight to find and fight the final Grimmkin, the Nightmares. Defeating these and returning to Grimm initiates the Troupe Master Grimm boss fight. The first Grimmkin fought are the Novices, and once all three are defeated, returning to Grimm upgrades the Grimmchild and allows for fighting the next Grimmkin, the Masters. Speaking with Grimm grants the Grimmchild Charm, and, as long as it is equipped, it is possible to fight the Grimmkin, scattered across Hallownest and take their flames (marked on the Knight's Map). When returning to Dirtmouth, two tents of the Grimm Troupe have appeared, with the larger one containing Grimm.

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