Brian Lumley deities
The title monstrosity of Lumley's "The Kiss of Bugg-Shash", Bugg-Shash is a gelatinous creature with innumerable humanlike eyes and mouths within its black mass. It attacks human victims by wrapping its mass around them and drowning them in slime, often attacking several individuals at once. Once dead, the victim(s) can be controlled, puppet-like, to perform a task where there is light, something that Bugg-Shash can not endure. Bugg-Shash is a name which Lumley first mentioned in passing in his early story "Rising with Surtsey", and later applied to the nameless creature of David Sutton's "Demoniacal" when he wrote "Kiss" as a sequel to it.
Kthanid is said to be the "brother" of Cthulhu. He looks like his sibling but has golden eyes. He resides in a crystal cave on Elysia. It is said that he is as good as his brother is evil. He bears a great hatred for the old ones for they had killed his family while he lay sleeping.
It first appeared in Lumley's 1975 novel The Transition of Titus Crow, and appeared again in his The Clock of Dreams (1978).
Mnomquah, the Lord of the Black Lake, is first referenced in Lumley's short story "The Sorcerer's Book" (1984). Mnomquah is trapped inside the Dreamlands' moon, though how he became imprisoned there is not known. He appears as a vast reptile with a crown of snaking feelers and empty sockets in place of eyes (though they still serve as sensory organs). His mate is the repulsive Oorn. It is said that when the other Great Old Ones return to lay waste to the world, Mnomquah will be reunited with his bride.
Mnomquah is called the Lord of the Black Lake because he rules over the Lake of Ubboth beneath the surface of the moon.
Oorn is mentioned in the book Mad Moon of Dreams (1987) by Brian Lumley. She is the wife of the reptilian Mnomquah. She has the form of a huge tentacled mollusc with snaking appendages that can spew digestive fluid on things she wishes to eat. Like her husband, her only true worshippers are the Men of Leng and the Moon-beasts. A temple devoted to Oorn and Mnomquah is near Sarkomand in the Dreamlands.
Shudde M'ell is "a great gray thing a mile long chanting and exuding strange acids... charging through the depths of the earth at a fantastic speed, in a dreadful fury... melting basaltic rocks like butter under a blowtorch."  Shudde M'ell is the supreme regent of the chthonians, a horrifying race of burrowing creatures, and is probably the largest and most malignant member of his kind. According to some legends, he was once imprisoned beneath G'harne, but now he is free to wander the earth with his kin.
Summanus (Lord of Hell, Monarch of Night, The Terror that Walketh in Darkness) is the creation of Brian Lumley — who based the Great Old One on the Roman deity of the same name — and first appeared in Lumley's short story "What Dark God?" (1975). The god appears as a mouthless human with whitish tentacles hidden under his clothing. He can use these tentacles to siphon blood from his victims.
Summanus had a following in Roman times, but if he is worshiped today, his cult is even more secretive. The rites needed for the proper worship of Summanus are found in the Tuscan Rituals.
Yad-Thaddag is possibly the Elder God equivalent of the Outer God Yog-Sothoth. This being has the same appearance as Yog-Sothoth, except its spheres are of a different color and its nature is purely benevolent. It appears in Lumley's 1989 novel Elysia.
Yibb-Tstll (The Drowner) is an obscure god, said to watch at the center of all time as the universe revolves. Because of this insight, only Yog-Sothoth is said to be wiser. Its blood, the Black, is a weapon which takes the form of black snowflakes that stick to and smother a victim. This is stated in The Caller of the Black. The god's touch causes an instant change in the person affected—this change is usually fatal but occasionally brings some benefit.
Yibb-Tstll is sometimes described as an immobile, dark, tentacled entity with a pulpy, alien head, detached eyes, and large bat wings under which countless Nightgaunts suck black milk from its innumerable breasts. In Brian Lumley's short story "Rising with Surtsey" (1971), the narrator proclaims: "... I wanted to bound, to float in my madness through eldritch depths of unhallowed black blood. I wanted to cling to the writhing breasts of Yibb-Tstll. Insane....". Yibb-Tstll makes its major appearance in The Horror at Oakdeene though an avatar or incarnation figures in Hero of Dreams.
Having a close connection to the Great Old One Bugg-Shash, so should Yibb-Tstll be regarded as a Great Old One - specifically in the Drowners group introduced by Brian Lumley, parasitic alien entities which thrive by vampyrizing the Great Old Ones themselves - though in RPG materials she is classed as "Outer God".