Nightmare King Grimm

"Twisted spectre of scarlet flame. "The expanse of dream in past was split, One realm now must stay apart, Darkest reaches, beating red, Terror of sleep. The Nightmare's Heart.""

- Seer

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
Having Grimmchild equipped is required to start the fight.

The fight functions similarly to the Dream Bosses. The base fight remains similar, although it is much faster paced, and most attacks gain new properties:


 * Fire Bats: Now, Nightmare King Grimm will send out 4 Fire Bats instead of 3. They travel in a pattern: first and third bats go high, second and fourth go low, with a wide gap in the middle. If the Knight gets within his arm's length before he ends the attack, Nightmare King Grimm will teleport and send 2 more Fire Bats, one high and one low, simultaneously.


 * Dive Dash: During both dive and dash, Nightmare King Grimm is followed by a flame tail that deals damage. The Flame Trail generated by the dive will disappear after he lands on the ground.


 * Dash Uppercut: The pause before Nightmare King Grimm launches himself into the air is shorter. NKG will burst six fireballs instead of five.


 * Cloak Spikes: The spikes will become dangerous in a shorter amount of time. Nightmare King Grimm is not present during the attack


 * Flame Pillar: Nightmare King Grimm summons 4 large pillars of flame. He remains stationary in the air throughout the attack. The pillars are summoned one after another. Each pillar starts forming where the Knight was and reaches the top of the arena. As a pillar begins to blench away, a wide, shorter flame appears and remains on the ground for 1 second.


 * Flamespawner: The Fireballs travel at a considerably faster speed.


 * Teleport: Nightmare King Grimm will teleport to a random place in the arena to perform an attack.


 * Skitter: Nightmare King Grimm will skitter away from the Knight before starting an attack if they are too close to him. It may happen that NKG will begin to telegraph for one type of ground attack, skitter away, and change to another ground attack

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 Knight 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). Knights can follow this dash up with Descending Dark, Shade Soul, any Nail Art, or regular Nail strikes. If the second Fire Bat is jumped over, staying still on the ground will allow the next two bats to fly over the Knight without being damaged.


 * Dive Dash: Dash, walk, or jump to avoid the Dive once it starts. It is best to jump over the Dash. The Knight 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 Knight 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 Knight 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 Knight in a precarious position (to avoid damage in that scenario, jump straight up as quickly as possible). If Sharp Shadow is equipped, due to the increased dash distance, it would be wiser to dash straight through NKG. After dashing through him, dash back to the spot the Knight came from, which will now be one of the empty spots in between the incoming fireballs of the second part of NKG's attack.


 * 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 Knight 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 Knight 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 Knight 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 Knight 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 Knight 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 Knight 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 Knight 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 Knight 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 Knight 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 Knights 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 Troupe Master 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.
 * Nightmare King also has 6 legs when he uses the Skitter manoeuvre compared to Grimm's 4.
 * 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 heart's 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.

Король кошмара Grimm Re dell'Incubo