Nightmare King Grimm

Nightmare King Grimm is the optional final boss of the Grimm Troupe in Hollow Knight. It is the Dream form of Troupe Master Grimm.

Behaviour and Tactics
Similarly to the first battle, it's all about reading what attack is coming and knowing how to dodge and/or retaliate. The only catch is that he is much faster this time, the windows for attacking him are smaller (or in case of Cloak Spikes, completely removed), and Nightmare King deals two masks of damage opposed to Grimm's one mask of damage. Shade Cloak can be invaluable for this battle, as the player can dash through most of Nightmare King Grimm's attacks if timed properly.


 * Fire Bats: Short jump over the 2nd Fire Bat and then dash while in the air to avoid the 3rd and 4th Fire Bats (this is safest with Shade Cloak). Players can follow this dash up with Descending Dark, Shade Soul, any Nail Art, or regular Nail strikes.


 * Dive Dash: Dash, walk, or jump to avoid the Dive once it starts. It is best to jump over the Dash. The player can also time a down strike on Nightmare King while he's dashing, or Great Slash to stall in the air and hit NKG as he stands up. Double jumping, while NKG is dashing, allows the player to stay aloft long enough to avoid the flame trail.


 * Dash Uppercut: If possible, dash away from NKG, then attack or Great Slash him when he finishes his dash and before his leap into the air (or hit him with Abyss Shriek). If there is not enough room in the arena to dash away from him, the player will have to pause and wait for about half a second before trying to shadow dash through him. Otherwise, he will skitter away and leave the player in a precarious position (to avoid damage in that scenario, jump straight up as quickly as possible). This scenario is all the worse when using Sharp Shadow due to the increased dash distance.


 * Flame Pillar: There are many options here. Slowly move in one direction so pillars will erupt behind the Knight, try avoiding being stuck in a corner of the arena (if necessary Shadow Dash through a Pillar). With this method, try to strike NKG a couple of times with the Nail. And/Or use Great Slash. Or double jump and downward slash to bounce on Nightmare King Grimm, moving left or right as necessary to avoid the next Pillar(s). Abyss Shriek is also good to use after the fourth pillar has started.


 * Pufferfish: It is best to stay close to the wall but not to stick to it as the player needs to move back a little to dodge a fireball. The best way to dodge this without taking damage is to make small jumps so the player doesn't accidentally hit the fireballs flying over their head. Another way is to climb the wall and jump onto to Grimm and use down strikes to bounce on him. Though to do this the player must take damage to take advantage of the invincibility frames or be really quick as soon as he starts the attack. With proper timing and a bit of luck, Shade Soul and Abyss Shriek can be useful here.

Healing : Without any healing charms, the player can heal: once right after the last flame pillar begins to form, once by jumping over one firebat and then immediately healing (the next low firebat will have had its flight pattern altered by its homing ability and will fly over the Knight's head, allowing time to heal possibly even twice) or as quickly as the Cloak Spikes attack starts though the timing on this combined with the positioning aspect makes it more tricky. Three heals are also possible during the stagger as long as the player starts healing as soon as the stagger starts and is prepared to move as soon after the third heal.

Shape of Unn can be used to heal under the Firebats attack as long as the player immediately starts healing once the attack starts (as the animation to transition into a slug takes enough time that healing too late will cause the player to be hit instead). In addition healing in cape spikes is made easier with Shape of Unn and healing is possible during the Flame pillars attack with the same conditions as healing during the Firebats attack.

The player can also heal by dashing away from his uppercut usually putting them in a safe position and immediately heal. The combination of Quick Focus and Deep Focus allows the player to heal 2 hitpoints at a time during all of these no-charm healing opportunities.

Charms : Dreamshield blocks the Firebats attack.

Sharp Shadow helps with attacking during the Firebats attack since the Knight's dash is slightly longer and it's easier to hit Nightmare King Grimm from farther distances. Sharp Shadow is a double-edged sword if used with improper spacing because the Knight will end their dash in Nightmare King Grimm, resulting in taking damage.

Nailmaster's Glory, Fragile Strength / Unbreakable Strength, and Mark of Pride can be very helpful for reaching and damaging him.

The Minion Build is a popular option, allowing players to focus on dodging. And Weaverlings can damage Nightmare King Grimm during the Pufferfish attack. The Minion build (in full) is Weaversong, Glowing Womb, Grubsong, Sprintmaster, and Defender's Crest.



Location
After defeating Grimm, he upgrades the Grimmchild, allowing the Knight to collect another four flames. After collecting at least three of them, Grimm will be asleep at the back of the large tent in Dirtmouth. After using the Dream Nail on him to enter his nightmare, the Knight must fight him, and complete the ritual.

Trivia

 * Other than the Radiance and Absolute Radiance, Nightmare King Grimm is the only other boss to have a fullscreen title card at the beginning of its fight.
 * When fighting Nightmare King Grimm in Godhome, his title card appears on the bottom of the screen, making him the only boss to have both a regular title card and a fullscreen title card.
 * The Grimmkin Nightmare watching in the background will rear back and 'laugh' whenever Nightmare King does the Flamespawner attack and after Nightmare King Grimm has been defeated.
 * Nightmare King Grimm looks nearly identical to his physical world counterpart Grimm (save for the red colour scheme), however, Nightmare King's horns are slightly longer.
 * An alternative way to predict Nightmare King Grimm's health is to observe the background as it changes per each Flame Spawner attack. At 75% health the heart beats faster, at 50% the hearts eyes glow red and at 25% the heart beats ever so faster and the glow becomes more intense.
 * A red barrier will appear over Grimm when trying to enter the fight without Grimmchild equipped.
 * In Godhome, it is not required to have the Grimmchild charm equipped to fight Nightmare King Grimm, this is also true for Grimm. However if equipped the Grimmchild will not be present for the fight.

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