The Underground Hallow is a Biome within the Underground layer which forms naturally as the Hallow spreads to the underground. This biome is defined by the presence of large amounts of Pearlstone Block within the underground layer. The Underground Hallow features several mobs unique to its environment, all of which naturally give off light.
Monsters that die within the Underground Hallow have a chance to drop Souls of Light. This applies to both monsters unique to this biome, as well as any from other biomes that may happen to wander into it. The Underground Hallow is also the only biome where it is possible to find Crystal Shards, which will grow on any Pearlstone surface except floors.
List of monsters unique to the Underground Hallow:
- Chaos Elemental
- Illuminant Bat
- Illuminant Slime
- Enchanted Sword
- Spectral Elemental (Console only)
- Hallowed Mimic (PC Only)
List of other monsters which may also spawn within the Underground Hallow:
- The Underground Corruption commonly clashes with the Underground Hallow, resulting in the player encountering monsters from that biome while still within the Underground Hallow. This concept also applies to other biomes (see Overlapping Biomes for more details).
- Hallowed or Corrupt Deserts may also be naturally present within or adjacent to the Underground Hallow, causing the Light or Dark Mummy to spawn.
- If Hell is close to hallow, Enemies spawned in it can drop souls of light.
- It is common for the Underground Hallow to spawn above the area you killed the Wall of Flesh at.
- Hallowed Mimics are a very dangerous monster to come across when exploring the Underground Hallow, as they can enter a defensive stance which will reflect any and all spells and projectiles while making them invulnerable. They also have a stomp attack where they jump directly over the top of a player and then hurtle towards the ground.
- Added to the game.