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Hell Slime is an odd Material that applies the Slime stain when touched. It is bled from Hell Spitters and spawns in naturally-occurring deposits in The Work (Hell) and The Work (Sky). It has several variants, not all of which seem to be used in game.
Hell Slime is primarily seen as the blood material from Hell Spitters, although it is unlike most blood materials in that it is similar to a solid variant of Fungus. It will form tall peaks and not flow like other liquids or powders due to its exceedingly high viscosity. It is also solid to most entities, leading the Hell Spitters to sometimes encase themselves in their own blood and suffocate.
Like Fungus, Hell Slime can fall through the air if there is no terrain supporting it, and it can sometimes fall into pools of Water where it will settle to the bottom and gradually dissolve, much like Slime does.
When landing on Lava, it will gather on the surface, providing a solid landing for creatures to walk on. However, when Lava is poured into Hell Slime, the slime will simply move out of the way, similar to how Clouds interact with liquids.