Zef's Nether is a mod that adds some cool new biomes to the Nether.
We have the Tyrian Forest, a third variant of the nether forests that is purple. It has its own corresponding wood type.
We have the Sulfur Fields, a yellow, hostile environment crawling with Magma Cubes and sometimes blazes.
We have the Metallic Dunes, a gray, sandy chasm containing Copper and Sparkers. Use Bottled lightning on a Sparker, and you'll get a Lightning Wraith.
And finally, a mysterious outbreak of the Wither effect...
Zef's Nether Team
