Grimm

After the Grimm Troupe has been summoned, Grimm can be found inside the large building at the center of their setup to the left of Dirtmouth. Inside, after talking to him, he gives the Knight the Grimmchild charm. After collecting three flames, he upgrades the charm to the next level, and after collecting three more, the Knight must fight Grimm.

Behaviour and Tactics
Before the battle, Grimm will bow. If the Knight hits him while bowing, Grimm will screech at the Knight and will counter attack with the Flame Spawner attack.


 * Firebats: Grimm opens his cape and three red firebats are summoned out at head level, flying in the opposite direction with slight homing onto the Knight. Each firebat also spawns a fire pillar on top of Grimm.


 * Firebat Teleport: Getting into melee range before the 3rd firebat causes Grimm to teleport to the other side of the arena and fire a single firebat.


 * Dive Dash: Grimm appears near the top of the arena, turning his body into the shape of a drill, diving towards the ground, then dashing a long distance in the direction of the Knight.


 * Dash Uppercut: Grimm appears at one side of the arena, dashes at the Knight, and uppercuts into the air, disappearing, and leaving behind six flames which fall to the ground in parabolic arcs.


 * Cloak Spikes: Grimm's cloak drives into the ground, and summons spikes made of his cloak around the arena, which rise up to near the top of the arena.


 * Flame Spawner: Grimm puffs up his body into a red sphere, floating in the center of the arena. He spawns red flames which can come out in several orientations. He cannot be hit by Nail strikes when he is in this mode. Grimm uses this attack once each at 75/50/25% health.


 * Evade: Occasionally if The Knight gets close to Grimm before his grounded attacks begin, he will scurry away and then do an attack.


 * Stagger: Every 13 hits, Grimm will explode into a horde of bats. Grimm can be damaged in this state, taking the form of the bat with eyes. However, he can only take a maximum of 50 damage per stagger.

Grimm is one of the fastest bosses in the game, and his health scales with your nail upgrades, making him a tough foe regardless of experience or progress.

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 6 projectiles as they spread in a cone pattern,this also gives healing opportunity especially with Quick Focus.

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

During the cloak spikes attack, The Knight can use the time to heal an extra mask. This is easier to do with Quick Focus.

Double jump and dash over his Firebats, and you'll be in range to attack.

Trivia

 * At the beginning of the battle Grimm will bow, if he is attacked before he can finish the bow, he will screech and immediately start his Flame Spawner 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.


 * When Grimm performs the Firespawner attack, the theme gets more dramatic by adding chorus to background.


 * The Grimmkin audience watching give ovation to Grimm every time he performs Fire Spawner or reforms after stagger.


 * When Grimm reforms after stagger, he is accompanied with a drumroll.


 * There is a secret area in Grimm's tent above the arena where the empty masks of the audience 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.


 * Some of his attacks, especially his Firebats, seem to be referencing attacks used by Dracula in the Castlevania series.


 * There is some speculation as to what species of bug Grimm is supposed to be:
 * It is possible that he is a bat due to the fact that he sleeps upside down and generally resembles a vampire.
 * In a response 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.”


 * Even in Godhome, it is not possible to fight him with Grimmchild. If equipped, it will not be present for the duration of the fight. The same is true for Nightmare King Grimm

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