Tortured Soul

The Tortured Soul is an uncommon enemy found in The Underworld only during Hardmode. If you throw Purification Powder on him, he will become the Tax Collector NPC. Only one Tortured Soul may appear at a time, and they will not appear if the Tax Collector has already been saved. If the Tax Collector is killed, he will respawn naturally without the need to purify another Tortured Soul.

Tips

 * The easiest way to find the Tortured soul is to use a long bridge in The Underworld. This way you have an easy path to find him, and gives him a better area to spawn. It is best to use the bridge used for the fight with the Wall of Flesh.
 * If you can hear doors being opened or closed, the Tortured Soul is nearby, as it is the only enemy in The Underworld that has the ability to open and close doors.
 * If you don't have a free NPC home available, the Tax Collector will move in as soon as you build a new one, as long as you purified a Tortured Soul.

Trivia

 * The Tortured Soul may serve as a reference to the character of Jacob Marley from the book A Christmas Carol. Both appear to be "tortured souls", hence the name, and both sport what appear to be metal chains from their wrist. Notably, in life, Marley worked alongside Ebenezer Scrooge as a very hard-nosed money lender - similar in tone to the NPC that the Tortured Soul becomes when exposed to Purification Powder.

History
Âme torturée