Also known as the Fungi from Yuggoth, the Mi-go are one of the most important non-human species in the Delta Green universe. They are the one alien race that has the most contact and influence on current world affairs. The fact that they are truly 'alien' makes the struggle against them more intense.

They are roughly man-sized, but shaped vaguely like insects. They have several sets of limbs, including large, leathery-looking wings. Their hands look like lobster claws. Their heads are elliptical, and glow with a variety of colors. It seems that these colors make up at least part of their language.

They first came to Earth from Yuggoth 160 million years ago, during the Jurassic period. It is thought there are certain minerals that they can only find on Earth, which is the reason they remain here, but the real reason may have to do with hypergeometry or the study of terrestrial biology. Over the eons, they have cultivated a small number of contacts with other species on Earth, including humans.

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