Cursed Crystal Caves is a secret dark transition level between the Scrapyard and the Frozen City. This area is different from regular Crystal Caves in regards that the color scheme is inverted. The wall and floor tiles are orange, the wall crystals are purple. The floor is sometimes completely covered in cobweb, sometimes there's no cobweb at all. The Crystal Spiders and Laser Crystals change into their cursed variations: Cursed Crystal Spiders and Cursed Laser Crystals. They are purple instead of orange, and emit purple smoke particles. They have the same amount of HP and deal the same amount of damage, but have some unique abilities that make them harder to deal with.
Cursed Crystal Caves are treated as 4-1. After clearing this area you continue to 5-1 in the Frozen City, and the game's difficulty remains unchanged.
Cursed Crystal Caves always have a Large Cursed Weapon Chest, which appears only in this level. It contains 3 Cursed Weapons that can be from 5 difficulties higher. If Cursed Crystal Caves are treated as 4-1 in terms of difficulty, this chest can drop weapons that are found in regular Weapon Chests in 7-1.