Torment League Guide

Tormented Spirits were introduced in Path of Exile in Patch 1.3.0 on 12/13/2014 with the Torment League. They are green ghosts roaming around randomly. When you get near them, they flee away from you. Those spirits can buff monsters with special abilities and increased Life/Attack/Cast/Movement Speed when they go through them (Spirit's Touch) or possess a Rare or Unique monster (Spirit's Grip).

Those buffs greatly improve the threat of touched and possessed monsters, especially since several Tormented Spirits can touch or possess the same monsters, stacking their buffs. The Tormented Martyr is one of the most dangerous ghosts (if not the most) as it can cast Detonate Dead, potentially one-shotting you if you don't have a corpse removal mechanic at your disposal.

Possessed monsters have increased Item Quantity and Item Rarity. The modifiers granted by Tormented Spirits to monsters are highlighted under their healthbar in light green. More often than not, you end up killing Tormented Spirits before it gets a shot at running away and buffing other monsters (and usually even before you see them).

Some Spirits guarantee special drops from the possessed target, such as Tormented Embezzler granting currency drops. Killing a Tormented Spirit or a possessed Rare/Unique guarantees some rare item drops. Lastly, Tormented Spirits that find no target eventually end up vanishing without leaving any loot. You can find a complete up to date list of all Tormented Spirits following this PoEDB link.

Unfortunately these days, Torment is pretty outdated and unrewarding, requiring very specific strategies revolving around Sextants and the Atlas Notable Seance to get a reasonable return.

Tormented Spirits can spawn randomly in any map including the Campaign. The Unique Boss of Shore Map, Belcer the Pirate Lord (based on Fairgraves) spawns a Tormented Spirit at 75% and 50% HP. However there are also plenty of mechanics to encounter them in your maps:

Scarabs

Sextants
There are a few Sextant modifiers adding Tormented Spirits in your map:

The best way to run these Sextants Modifiers is to use them on Maps with 3 Bosses (like Courtyard) alongside the Atlas Notable Seance so you don't have to worry about letting Tormented Spirits possess monsters to reap your rewards! Eventually you can use the Enthralled Map Modifier (see below) on the Maps for the same result.

Map Mod
There is a Map Mod (Enthralled) stating Unique Bosses are Possessed, which makes all Map Bosses from the map possessed by a Tormented Spirit.

Map Enchant
Harvest can offer you to enchant your maps with the Vivid Nestback seed. The most common enchant from this seed allows you to interact with Tormented Spirits: Map boss is surrounded by Tormented Spirits, spawning a dozen of Tormented Spirits around the Map Boss.

Incursion Room
There is an Incursion Room themed around Tormented Spirits:

Strongboxes
The Unique Strongbox Ashes of the Condemned has an exclusive modifier: Guarded by a stream of Tormented Spirits. This mod releases numerous Tormented Spirits one by one over time.

Delve
In Delve you can find the Haunted Tomb room in the Fungal Caverns biome, which is themed around Tormented Spirits and guarantees a Tangled Fossil drop.

Rituals
The Haunted Ritual has the unique modifier Tormented Spirits haunt the Ritual which spawns Tormented Spirits during the Ritual.

Torment brought some exclusive unique items which are now part of the core drop pool, meaning they can drop anywhere in the game.

You can find quite a few passives and notables related to Tormented Spirits spread in 2 wheels in the Atlas Passive Tree:

Unfortunately, Torment is an outdated and irrelevant mechanic by current Path of Exile standards. It only brings flavor in various mechanics without any specific reward besides its special Sextant modifiers, which require you to specialize into Seance on the Atlas Passive Tree.