During the limited edition Bloody Harvest event in Bordlands 3, Haunted Enemies has a small chance to spawn in the game. These are kind of like a reskin of regular enemies, but have some extra types of attacks that they can use when attacking the player. The Haunted Enemies can spawn at any point in the entire game, and every single enemy has a chance to spawn as a Haunted version of that enemy. So you will come accross a lot of Haunted Enemies randomly by just playing the game after having started the Bloody Harvent event.
That said, there are methods to find Haunted Enemies much more quickly than just randomly looking for them. Certain areas in the game has a very high chance to contain many Haunted Enemies, and the three following areas have been confirmed to be like that:
- Circles of Slaughter.
- Coracious Canopy.
- Lectra City.
So if you are looking to farm Hecktoplasm or just loot from the Bloody Harvest event, there 3 areas are your best bet.