Leech of Yoh-Vombis
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A Leech of Yoh-Vombis is a parasitic creature native to Mars. In appearance it is a shapeless sluglike dark creature, like a flexible hood or flattened jellyfish. The creatures were introduced "The Vaults of Yoh-Vombis (fiction)" by Clark Ashton Smith, where human archaeologists found the creatures entombed in a vault within a ancient Martian city. The organism can apparently glide through the air, envelope the head of a humanoid victim like a cowl, digest the skull and brain, and assume control over the body. The only know way to remove them is to aggressively attack them with a knife as soon as they attach themselves.