Grimm

Troupe Master Grimm is both a quest character and boss introduced by the Grimm Troupe in Hollow Knight. He is the main character behind his quest. Nightmare King Grimm is his Dream form.

Lore
Grimm is the master of the Grimm Troupe, a mysterious travelling circus. In truth, Grimm and his Troupe travel from the Nightmare realm to wherever the Nightmare Lantern has been lit by acolytes. They gather Nightmare Flames from ruined lands to fuel the sinister being enslaving the Troupe, the Nightmare Heart.

The Troupe Master has a charming and playful personality. As the Nightmare King, however, his self in the Nightmare realm, his thought are focused on his enslavement to the Heart. Their ritual to feed it consists of feeding first a Grimmchild with Nightmare Flames. They then slay the Nightmare King for it to be reborn anew through the Grimmchild.

Hollow Knight
Grimm and his Troupe set up tents in Dirtmouth as soon as the Knight has lit the Lantern. Inside the main building, he appears to them in a show of red light and smoke. The Troupe Master is aware that the Knight called them with he Lantern and offers them to participate in their ritual. He then gives them a Grimmchild and entrusts them to collect the Nightmare flames gathered by his Grimmkins throughout Hallownest.

With each set of three flames gathered, Grimm has the Grimmchild consume them to grow. After the second set, the Troupe Master tests the Knight's strength in a fiery, theatrical battle, in preparation for their confrontation with the Nightmare King. He also rewards them with a Charm Notch.

After collecting the third set of flames, Grimm will be found sleeping in his quarters. As such, he is ready for the Knight to use the Dream Nail on him and enter the Nightmare realm. If they successfully slay the Nightmare King, the Troupe will have completed their ritual and leave Hallownest before the Knight wakes up. The Troupe will also disappear if the Knight helped Brumm banish them instead of facing the King.

Grimm can be summoned to Godhome by  the Godseeker's own ritual. There he will be conscious of his surroundings and delighted to participate, even though he is not native of Hallownest. He takes part in both the Pantheon of the Sage and the Pantheon of Hallownest. In the latter, the Nightmare King appears as one of the last three Gods at its peak. Even though away from the Nightmare realm, the Heart still watches over the Nightmare King's fight.

Behaviour and Tactics
Because Grimm moves by way of teleportation and rarely stays in one place for long, from an offensive perspective, it's important to deal as much damage to Grimm in the shortest time possible.

Each spell has its use against Grimm. Vengeful Spirit is useful to use during the Cloak Spikes, Pufferfish Attacks and Fire Bats Attack. Desolate Dive is a great way to dodge the Dive Dash Attack. It's best to use it almost as soon as the Knight sees Grimm preparing the Dive Dash Attack because Grimm will land in the middle of it. Howling Wraiths can be useful during a Flamespawner Attack right before the fireballs start to spawn and during a Cloak Spikes Attack since Grimm is taller than the Knight.

The Nail Arts Great Slash and Dash Slash are also useful, providing 2.5x Nail damage and good range for damaging Grimm and staying safe (especially during Cloak Spikes, Dash Uppercut, and Fire Bats Attacks).

Use the Shade Cloak to dash through both of his Dash attacks (Dive Dash and Dash Uppercut). The Knight can also damage Grimm this way if they have Sharp Shadow.

Standing directly next to where Grimm explodes into fire when he uses Dash uppercut is a good way to avoid all 5 projectiles as they spread in a cone pattern, this also gives healing opportunity especially with Quick Focus.

During the Cloak Spikes attack, The Knight can use the time to heal. This is easier to do with Quick Focus.

Shape of Unn is a fantastic way to heal against Grimm. The charm lowers the Knight's hitbox so the Knight can heal safely during a Fire Bats Attack. If combined with Quick Focus, the Knight can run and heal from Grimm during a Dash Uppercut Attack too. It can also be used to heal and position at the same time during the Cloak Spikes attack.

If the Knight stays near the right/left side of the screen and light tap jumps, they can mostly avoid the flames during Grimm's Flamespawner Attack.

Double jump and dash over the Fire Bats, putting the Knight in range to attack.

It is possible to defeat Grimm under few seconds only using Abyss Shriek in conjunction of Spell Twister, Shaman Stone & Stalwart Shell. While having all 3 Soul Vessels (Having Coiled Nail or higher, otherwise 2) fully filling them by Dream Nailing creatures from Forgotten Crossroads then when the fight starts hitting it while bowing to make it start his Flamespawner attack, quickly get under it and repeatedly using Abyss Shrieks. If the Knight does not have the required number of Soul Vessels, they can wear Grubsong to regain some soul by taking damage to use the final Attack. Using this won't let Grimm use any of its other attacks. According to the Nail upgrade, the number of uses varies:
 * Having Channeled Nail or lower upgrade, have to use 6 times.
 * Having Coiled Nail, have to use 7 times.
 * Having Pure Nail, have to use 8 times.



Trivia

 * Grimm always bows to the Knight before the start of the fight. If struck when bowing, he screeches at them and starts the Flamespawner attack.
 * When fought in Godhome, Grimm bows to the Godseeker instead of bowing to the Knight.


 * The Grimmchild charm is required every time to start the battle, except in Godhome.
 * Grimm is the only Boss to have music variations and audio cues for some events:
 * When Grimm performs the Flamespawner attack, the theme gets more dramatic by adding chorus to the background.
 * The Grimmkin audience watching gives an ovation to Grimm every time he performs the Flamespawner attack or reforms after stagger.
 * When Grimm reforms after stagger, he is accompanied by a drumroll.
 * Varying cues are also triggered during his fight in Godhome.
 * There is a secret area in Grimm's tent above the arena where the empty masks of the audience, some chests, and a strange device can be found. It can be accessed by wall climbing through a false ceiling to the right of the arena, second arch.
 * When using a spell in this secret room some sort of barrier appears which may possibly be related to a Seal of Binding.
 * In a response to a question on Grimm's character inspirations in one of their Hollow Knight streams Team Cherry has stated:
 * Can you confirm Grimm was inspired by Dracula from Castlevania?

William: "He’s like a mix of a lot of things." Ari: "Yeah, he has this kind of circus master quality, and-" William: "Halloween-y.. He’s spooky."
 * Ari: "I don’t think- I mean Grimm obviously has a lot of Dracula-like qualities. But he also has other elements."


 * In Godhome, it is possible to fight Grimm (and his dream form Nightmare King Grimm), without the Grimmchild charm equipped. If the Knight chooses to use the charm, the child will not appear to aid the Knight in the fight.