One of the mobs added with Nether X is the inferno spider. These little spiders are weaker than nether spiders, but that does not make them any less dangerous. When they attack you, they will light you on fire. They can be pretty hard to fight without magma armor. The inferno spiders will only spawn in the soul sand desert biome and maybe the mysterious nether dungeons.
Drops: string, spider eyes, and rarely blaze powder.