Uumuu

"Intelligent being that guards the inner chamber of the Teacher's Archives. The canyon below us, the one thick with fog and crackling with strange energy... a Hunter can lose their senses down there. Be careful... strange and unnatural things lurk there."

Uumuu is a main boss in Hollow Knight. It guards Monomon the Teacher, one of the Dreamers.

Lore
Uumuu is an intelligent yet Infected being similar to the Uomas and Oomas infesting Fog Canyon. It defends Monomon's chamber at the heart of the Teacher's Archives.

In-game events
Uumuu appears from the acid pool in the room preceding the inner chamber once the Knight reaches it. During the fight, Quirrel intervenes to strike Uumuu with his nail and break its gelatinous defence, exposing its core. Once defeated, the Infection bursts out of Uumuu before it explodes.

When fought in Godhome, Quirrel is not present. Instead, Uumuu summons Oomas to help it, but they can also be used to break its defence.

Behaviour and Tactics
Uumuu floats around the room and uses one of two attacks:
 * Burst: Uumuu fills the arena with small bursts of lightning. Each lightning burst lasts about one second. The lightning bursts appear in one of two patterns throughout the arena. The bottom platforms are always safe to stand on, with alternatively the top left or the top right platform being safe depending on the pattern. The lightning bursts become dangerous at different times. The entire attack lasts for about two and a half seconds.
 * Chase: Uumuu creates a small burst of lightning where the Knight is, similar to Volt Twisters. Uumuu continues to create a new small burst of lightning every second for about six seconds. Each burst persists for about two seconds. Each new burst appears where the Knight is, so constant movement is necessary.
 * Hover: While not attacking, Uumuu hovers around the arena, slowly chasing the Knight.

When initiating the fight, Uumuu can deal damage when it rises up from its resting spot within the acid.

Uumuu cannot be harmed normally, as its vulnerable core is protected by a membrane that deflects the Knight's attacks and shields it from Spells. However, after dodging attacks for a short time Quirrel appears to help the Knight, leaping around the battlefield and occasionally popping Uumuu's shield. This deflates Uumuu, leaving it open to attacks for about 5 seconds.

Although Uumuu only has two attacks, they are both quite hard to dodge, and leave few opportunities for healing. In addition, Uumuu's erratic movements and the very sparse opportunities for hitting it compared to its health pool result in a very drawn-out battle.

Get in as many hits as possible when Uumuu's shield is popped, and be prepared to dodge an attack right after. In desperate times, this can be an opportunity to heal instead. Avoid jumping in the acid below, as this greatly slows movement and causes damage if Isma's Tear has not been obtained.

As with most boss fights, the Quick Focus Charm is highly recommended. SOUL-generating Charms like Soul Catcher, Soul Eater, Kingsoul, and Grubsong are also very helpful in this fight, as chances to hit Uumuu, and consequently, chances to gather the SOUL needed for healing, are quite rare. The Great Slash Nail Art and the Pure Nail are recommended in order to make short work of Uumuu.

Uumuu can be completely killed by using the Abyss Shriek Spell three times with the Shaman Stone Charm, allowing it to be beaten in one cycle, given that enough SOUL has been gathered before the fight.

Using the Dream Nail on Uumuu is a good way to gain large amounts of SOUL, but it can be difficult to avoid getting damaged. Equipping the Dream Wielder Charm for this fight makes it easier to use the Dream Nail.

While in Godhome, in the Pantheon of the Sage or the Hall of Gods, Quirrel is no longer at the Knight's side to break Uumuu's protective membrane. However, Uumuu does gain a new attack that can be turned against it. Uumuu is also slower in this incarnation.

Uumuu has all the same attacks as its regular form with one new one, that can be used to make it vulnerable:
 * Summon: Uumuu emits a screech and summons two Oomas that slowly float up until they disappear from the top of the screen. The Oomas themselves pass through all platforms, but their cores, once exposed, explode if they intercept a platform. Getting these Oomas' explosive cores to collide with Uumuu breaks its shield while also dealing 50-150 damage to Uumuu. Uumuu is invulnerable to the Oomas while screeching to summon more.

There are a couple of methods of making Uumuu vulnerable:
 * Have the Knight at an angle where the Ooma is right between them and Uumuu, then strike the Ooma in Uumuu's direction.
 * If the Ooma is in close proximity to Uumuu or even behind/directly inside it, use a ranged spell such as Vengeful Spirit/Shade Soul to trigger the Ooma.
 * The trickiest method is to dispatch the Ooma while being between it and Uumuu, then kite out the homing explosive core so that it is guided into Uumuu.

Otherwise, the fight stays relatively the same, with the same dodging tactics.

Location
Uumuu is located in the centre of the Teacher's Archives.

Trivia

 * Nail-bouncing on top of Uumuu, while it is still invulnerable, launches the Knight a higher distance than usual.
 * Uumuu cannot be damaged by the Defender's Crest and Spore Shroom Charms.