Nether Biome: withering quagmire/morass

A swamp like variant of the upcoming nether forests. It should have a viscous black sludge, instead of water/lava, this sludge would deal wither damage to players and mobs. mobs that would die in the sludge become a withered variant. Withered variants have darkened skeletons (zombified piglin) and slightly darkened skin, they now inflict wither damage. "Trees" in the area could be petrified and or dieing.