Flukemarm

Behaviour and Tactics
An optional boss that floats in the center of the massive room, completely stationary, and continuously spawns quick and aggressive Flukefey from its orifices, two at a time, after spitting bile. Drops the Flukenest charm when defeated.

The boss itself does not attack, but spawns enemies that are really fast and frantic and can easily overwhelm the player.

An "offensive" tactic requires the Nail upgraded enough to kill Flukefeys in one hit, or using Fragile Strength. Focus on killing the Flukefeys as quickly as possible, and hit the Flukemarm between spawns.

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.

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 defenseless.