The Collector

An elusive being with a hobby more sinister than gathering harmless trinkets, it travels through the corridors of the dungeons, collecting the severed heads of fallen heroes he comes across.

A tall and terrifying figure – a King in Yellow, a Desecrator of Graves and Bodies, a Beheader of Corpses, a Taker of Heads. The Collector is shaped like a man, dressed as a man, has the face of a man, but the similarity ends there. What is hidden underneath that yellow cloak is an inhuman monster, a horrid amalgamation of severed heads and torn out spines twisted together into nightmarish mass of flesh and skulls. Just a glimpse underneath his cloak is enough to tell you what this thing has done to its victims and what may happen to you if he catches you. Where he comes from no one knows. Some believe that the Collector is the result of the ancestor’s many vile experiments, others that he is an otherworldly creature that sneaked its way into our world. In the end it does not matter, the only thing that matters is that he must be stopped before he desecrates more graves of your fallen heroes, cuts off their heads, and adds them to his macabre 'collection' of still living screaming heads and tortured souls.

Behaviour
The Collector is an Eldritch/Human miniboss who has a 5% chance to spawn if your inventory is over 65% full. It carries with it the Puzzling Trapezohedron, a gem worth 5000 gold, or one of three unique trinkets: Barristan's Head, Dismas's Head, or Junia's Head.

The Collector doesn't have the highest of stun resistances or speed; you should have a chance to stun him on first round before he uses Collect Call and damage him significantly.

Once Collect Call is used, target any Collected Highwaymen first, as he deals high damage and can inflict bleed. Stun Collected Man-at-Arms to break his guard on Collector or Highwayman, ignore Collected Vestal. The ideal composition to deal with is 2 Vestals and the Collector: Vestals don't have offensive abilities, you can out-damage their heals and sometimes they will waste their turn on buffing. From rank 3 the Collector usually uses his weakest move, Show Collection.

After the fight you can spend a few turns healing; Collected Vestals and Man-at-Arms are harmless.

Loot
There is a 3/4 chance for him dropping a Puzzling Trapezohedron and a 1/4 chance of him dropping one of the aforementioned Heads.

Abilities
COLLECT CALL: the more enemies that are on the field, the less likely the chance is for the Collector to use his "Collect Call". More specifically, the numbers are 1000x if no enemies at all (meaning he will virtually always open with this move), 9x and 3x for 1 and 2 enemies respectively. He will not use this skill if all ranks are covered.

SHOW COLLECTION: 3x chance for the Collector to use this skill.

LIFE STEAL: 2x chance of him attacking your heroes with this ability.

Note that there are no 1x numbers, that means, for instance, that should all ranks be occupied, 2 out of 5 times he will use "Life Steal" and the other 3/5 "Show Collection". If there are 3 enemies the probability should read: 2/9 for "Life Steal" and 1/3 for both "Show Collection" and "Collect Call". For 2 enemies, 1/7 will roll on a "Life Steal", 3/14 on a "Show Collection" and 9/14 on "Collect Call". If the Collector is alone, it is safe to assume he will be using "Collect Call".

* The possible summons are the Collected Highwayman, the Collected Vestal and the Collected Man-at-Arms ** While none of The Collector's attacks or those of his summoned heads deal extra damage against marked targets, it does allow the "Collected Highwayman" to focus his attacks on marked heroes.

Trivia

 * The Collector is a reference to Hastur, otherwise known as The King in Yellow.
 * The Collector also bears a striking resemblance to the Bloodborne character Micolash, Host of the Nightmare, who also has a cage affixed to his head.
 * The cage that the Collector wears was once a common form of torture employed for prisoners and lunatics. Spikes could be outfitted to the bottom of the cage to inflict additional pain on a subject being tortured should they attempt to crane their heads in response to pain. Additionally, some models featured sharpened spikes or spurs that projected from the horizontal cross-bars of the cage into the mouth, whereupon they dug into the tongue if the victim attempted to speak and were often fitted onto those accused of heresy or witchcraft. A variant called a "scold's bridle" or "the branks" was even employed to silence and humiliate housewives between the 1500-1700's by means of a curb plate which projected into mouth and pressed down upon the top of the tongue, preventing speech.
 * One of the trinkets dropped by the collector is called Dismas's head, so it can be inferred that it is the same head as your starting highwayman is called Dismas. However, you can find this trinket while Dismas is still alive.