Forgotten Madman

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Description

An enemy hunter wearing the Madman Set, will spawn an additional hunter once his health reaches a certain threshold.

At ~30% HP he will summon Madman's Escort (that uses Kirkhammer and Flamesprayer, so you have to deal with two enemies.
Uses an Empty Phantasm Shell to temporary buff his Ludwig's Holy Blade.
Fighting him is very similar to fighting the various enemy hunters during the story.
Unlocks the Madman Set at the Bath Messenger Insight after defeat.
He seems less likely to attack you near the Fog Wall (Entrance), luring him there is an easy way to get in several free hits.

Forgotten Madman

Madman's Escort

The first part of the battle is very simple. The madman usually starts of with slow and easily predictable two-handed attacks.
Use your gun to interrupt him and deal damage with visceral attacks.
Will cast tentacles when attacked at close range upfront, with long recovery time giving you a chance to dash out lots of damage.
Will cast magic missiles if you're far away. Can easily be dodged or avoided using the stone pillars (depending on the location you fight him).
Once his health reaches ~30%, he will spawn another hunter, the Madman's Escort that uses a Kirkhammer and Flamesprayer.
Try to separate them using the stone pillars on the room (depending on location) and finish the Madman.
Killing off the Madman's Escort is pretty simple, as he only uses the normal Kirkhammer attacks and spraying around flames. No magic attacks.