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The Hallow is a biome that is created once the Wall of Flesh in the Underworld has been defeated. It is an anti-Corruption biome and can be spread by planting Hallowed Seeds or throwing Holy Water, and is most effective when used to counter the spreading of Corruption; however, the corruption and hallow can still spread over each other, just very slowly.
The Hallow has its own, specialized underground level called the Underground Hallow. It is primarily made of Pearlstone, a white colored Ebonstone-like block converted from normal stone. Much like Ebonstone, Pearlstone takes longer to dig than normal stone, and requires at least a Nightmare Pickaxe.
The rules for spreading The Hallow are as follows:
- Pearlstone and Pearlsand Blocks will spread The Hallow to adjacent Stone, Sand, and Grass blocks (Pearlstone will not spread The Hallow to dirt blocks without Grass growing on them).
- When planted, Hallowed Seeds will spread The Hallow to adjacent Dirt, Stone, Sand, and Grass blocks.
- The Hallow cannot spread to/through:
- Mud Blocks; therefore it can't spread through the Jungle.
- Snow Blocks; therefore any Snow Biome is also safe. (As of 1.2, Ice Blocks can be hallowed, though)
- any gap (any direction) which is more than three blocks across.
- Note: Vines are still able to infect through proximity, so take caution.
- synthetic/non-infectable blocks which are three or more blocks across. This includes grassless dirt; If used with Hallowed Grass, however, it will simply spread like common grass over it, negating its effect.
- Sunflowers will not impede the spreading of The Hallow (neither pre- nor past-WoF).
- The Hallow can be planted in a world where the Wall of Flesh has not been killed but, similar to the Corruption/the Crimson, it won't spread through Sand and Stone. It will spread the Hallow grass over default grass, however. If the Hallow is created underground, Chaos Elementals can spawn, but neither they nor any other monsters will drop Souls upon death. Crystal Shards also won't grow in a world prior to Hardcore.
- While The Hallow does prevent Corruption from spreading, the creatures spawned within are still on-par with other Hardmode enemies.
- The Corruption may be completely removed from a world by spreading the Hallow with Hallowed Seeds, Holy Water, or by placing different Hallow blocks.
- Holy Water may be used to create the Hallow biome, even if no other Hallow biomes are present in the world.
- Unlike in both The Corruption and The Crimson, NPCs will not move out of their house if the Hallow spreads beneath it.
- The absolute best way to stay free from both Corruption and Hallow is to build houses in a Snow Biome. Snow Blocks are immune to both hallow and corruption; however, Ice Blocks are not. Since 1.2, the Snow Biome is now not entirely safe anymore as one must also take caution to avoid the Hard Mode monsters that reside in the Snow Biome, including Ice Golems, Wolves, and Ice Elementals.
- The Hallow shows some resemblance to the Forest in "The Lorax" by Dr. Seuss.
- Vilepowders in Terraria mobile show the tooltip: "Removes the hallow" but there has been no signs of the hallow.
- Added to the game.