Flukemarm

"An insatiable breeder. Has populated the Waterways with its kind. Its insides double as a nest for young Flukefeys. The desire to breed, to leave behind a memory of ourselves in the shape of a child... it seems to be etched deep into the heart of every living creature. I too have felt the pull of that base instinct."

Flukemarm is a hidden boss in Hollow Knight. Defeating her grants a new Charm.

Lore Flukemarm is the mother of all Flukes infesting the Royal Waterways. Her body is used as a nest for young Flukefeys. Like her children, she was infected and made hostile, although her condition as breeder prevents her from leaving her cave.

In-game events Flukemarm can be found suspended in a hidden cave below the pipework of the Royal Waterways. She lays dormant at first but will show hostility as soon as the Knight strikes her. Her defence relies on throwing Flukefeys at her foe.

When Flukemarm is defeated, the Infection within bursts out, making her explode. She leaves behind the Flukenest charm.

Behaviour and Tactics
Flukemarm has the following singular attack:
 * Spawn: Flukemarm will spit out two Flukefeys from either of its orifices telegraphed by bile spewing out of the selected ones. There can only be a maximum of 6 Flukefeys spawned at once.

An optional boss that is located in the centre of a massive room. She will remain passive and idle until provoked by damage. The Knight will also not be locked into this fight, meaning the player is free to escape anytime during the fight.

An "offensive" tactic requires upgrading the Nail enough (Nail Upgrade 3 or Higher) to kill Flukefeys in one hit or using Fragile Strength / Unbreakable Strength. Focus on killing the Flukefeys as quickly as possible and hit the Flukemarm between spawns.

Another "offensive" tactic is to gain SOUL from the Flukefeys, and then using Vengeful Spirit or Shade Soul to deal damage to Flukemarm continuously.

A "defensive" tactic involves using Quick Focus and Stalwart Shell to buy time, Soul Catcher and Grubsong to generate enough SOUL to heal, and Thorns of Agony to help kill the Flukefeys and occasionally damage the Flukemarm itself if the player is close enough to it.

Using Desolate Dive/Descending Dark is effective as the Spell gives enough invincibility to repeatedly use the spell without taking damage.

Abyss Shriek is very effective, especially when empowered by Shaman Stone. With this setup, three full casts without interruption will instantly kill Flukemarm.

The most important thing to avoid in this fight is falling into the water. Since the player cannot attack while swimming, they will be left completely defenceless.

Location
Flukemarm is located in a hidden area of the Royal Waterways. Desolate Dive/Descending Dark is needed to break the breakable floor which leads to this area. Flukemarm can be found at the end of a tunnel in the southwest.

Trivia

 * Flukemarm used to only use the ambient theme for the Royal Waterways. It has since been changed to the action theme.
 * After Flukemarm's defeat, the upper part of the body will be left in the arena. It can be attacked with the nail or with spells and can even be pogo'd on. However, this will not result in anything happening.

References

Тремоматка Tremarmita Maranide Madre Flukemarm Matka Przywr