The Collector

The Collector is an Eldritch/Human miniboss who has a 5% chance to spawn if your inventory is over 65% full. Drops Puzzling Trapezohedron, a gem worth 2500 gold, or one of three unique trinkets: Barristan's Head, Dismas's Head, or Junia's Head.

Strategy
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 Collected Highwayman first, as he deals high damage and bleeds you. 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 Collector, Vestals dont have offensive abilities, you can outdamage their heals and sometimes they will waste their turn on buffing, from rank 3 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.

Abilities
* The possible summons are the Collected Highwayman, the Collected Vestal and the Collected Man-at-Arms ** The Collector heals for the damage inflicted plus a small amount. It seems to be +5-10, most likely increasing with the difficulty of the dungeon. This needs confirmation, however.

Trivia

 * The Collector is a reference to Hastur, otherwise known as The King in Yellow.
 * 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 bridal" 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.
 * The Collector's "Life Steal" attack marks heroes. However, currently none of his attacks or the attacks of the collected heroes have attacks that take advantage of marks.