Underground Hallow

The Underground Hallow is a version of the Hallow that appears at the underground depth and below. Similar to Underground Corruption, Underground Hallow will spread through blocks that other Hallowed blocks come into contact with. Hallow is the only thing that Corruption will not spread through, and the opposite seems to be true.

In the Underground Hallow, there are some enemies that cannot be found anywhere else, all of which are very powerful. These enemies include: Illuminant Slime, Illuminant Bat, and Unicorns (which can also be found on the surface).

The Underground Hallow, as with the Underground Corruption, do not generate on new worlds, but rather when the world enters hardmode after the Wall of Flesh has been killed.