The Hollow Knights are known to be capable of moving through the different islands without requiring portals to do so. How they do this is currently unknown. It also appears that they have specialization in certain elements, are born/made with certain elemental affinity or adapt to their environment. They are most likely to be under the command of the Hollow King. The Sun appears to affect them significantly, making them teleport away and disappear during the day (except for lunar biomes where they can be found any time of the day). Some say that Hollow Knights are fallen Portal Knights.
Hollow Knights spawn in every island (with exceptions) during night. They have various level and element affinities (aka Damage Types) and are usually adjusting to the island's level and biome (there are various exceptions, though). Each type of knight has its own attack pattern and players should adapt when fighting them.
Hollow Knights are never listed on the List of Enemies on the player's map.
There are 6 primary types of Hollow Knights that the player will meet:
- Hollow Knight of Thunder
- Hollow Knight of Mist
- Hollow Knight of Frost
- Hollow Knight of Fire
- Hollow Knight Overlord
- Hollow Knight of Stars