The Moon-Beasts are “great greyish-white slippery things which could expand and contract at will, and whose principal shape, though it often changed, was that of a sort of toad without any eyes, but with a curious vibrating mass of short pink tentacles on the end of its blunt, vague snout". They live on the dark side of the Dreamlands' moon which, unlike the moon of the waking world, has great forests and oily seas.
The moon-beasts sail black galleys between the moon and the Dreamlands, trading rubies for slaves and gold at the port of Dylath-Leen. When there, they employ the Men of Leng, disguised in turbans, as their go-betweens and stay hidden below deck, lest the merchants of Dylath-Leen learn the terrible secret of with whom they are dealing.
The moon-beasts have a permanent settlement at the Nameless Rock, a jagged granite island near Inqanok in the Cerenerian Sea. Slaves are sometimes brought here for unguessable reasons. The Nameless Rock is superstitiously avoided by passing ships because of the strange howls sometimes heard there at night.