It would seem since its heyday when Lovecraft and his associated Authors penned the Mythos that such has culminated and thusly propagated into today's RPG Lores / Systems - though with adjustments and/or shifts the basis remains the same...

Definition

Chaos is associated to WHFRP and 40k

Horrors are associate to Earthdawn

Mythos is associated to Lovecraft / Cthulhu

Consensus Magic / Pattern Magic (Mage - WHitewolf / Fasa)

All in all - multi-dimensional beings who by the angles and stars pollute our material realm known as reality...

Anyone else blend such concepts - I did see mention of it in the Dark Heresy Forums not sure if Rogue Trader GMs do so as well?

On that note - is the Emperor really Nyarlathotep? (ROTFL)

My Campaign Definition

I have no problem blending all together - if I need to omit something then its justly in another dimension and poof - it gone from the campaign, otherwise the integration of Horrors / Mythos for me blends seamlessly and stumps veterans of the 40k Universe when they can't identify that servitor-race or god-power they come to meet with and challenge...

Where's Cthulhu then - sleeping his material form is like rock, once the stars align then his form will vibrate to our reality and thusly he will be made manifest (so atm he physically doesnt exist in my version of Earth/Terra - though a site comprising of the rocky stony stata by which he will inhabit does... aka his vessel)

IM40KU I always have the Cthulhu mythos in the back of my head. The Eldar Gods are the Elder Gods, the Outer Gods are the Chaos Gods, and the Great Old Ones are the C'tan. It's never come into play in a game of mine, but the idea is always there, tainting my plot devices, just like the idea that the Emperor is probably the most singly evil human being that ever drew breath. It will never come into play, but it colors my galaxy.

I seem to remember an adjunct writer that expanded the Cthulhu mythos burying some horror (Great Old One or Outer God?) in the core of the Earth. I'd probably make use of that suggestion as the Emperor as Nyarlathotep but as I said, I'd never use these a actual plot devices. They just color my universe. I've used Mi-Go as Yu'Vath before, and I'm doing it again. I just love the similarities. I'm still working out the Slaugth angle.

Personally I'm working on the life cycle of the Flying Polyp.

It starts off as Warp Coral, then grows to be Enslavers and finally becoming a fully fledged Flying Polyp.

These are warp entities but not in the same way that demons are in fact demons find them to be anathema. I'm even going so far to say that weapons forged from Warp Coral have the Holy quality against demons and stress the user's sanity but do not deliver any corruption points.

Nice idea. I like it. Flesh it out and I'll put them in my current campaign. They'd fit nicely.

I also want to get around to some exraterrestrial Serpent People, tie them in with some old Lovecraftian Yig's people crossed with R.E. Howard and others' King Kull, Kane, Bran Mac Morn, and Cormac MacArt stuff.

I seem to remember an adjunct writer that expanded the Cthulhu mythos burying some horror (Great Old One or Outer God?) in the core of the Earth. I'd probably make use of that suggestion as the Emperor as Nyarlathotep but as I said, I'd never use these a actual plot devices. They just color my universe. I've used Mi-Go as Yu'Vath before, and I'm doing it again. I just love the similarities. I'm still working out the Slaugth angle.

The Cthonians?

Nice idea. I like it. Flesh it out and I'll put them in my current campaign. They'd fit nicely.

Unfortunately due to various Real Life™ issues I'm putting development on the backburner for a while.

Here is what I've got in case people want to work with it.

• Warp Coral is the larval sta ge of the Flying Polyps, it exists in the Warp as shimmering reefs that ships can collide with. It can exist freely in real space. The most common way for this to happen is collisions. A ship that has had an impact with Warp Coral has a chance of ripping several crystals away from the reef and taking them with it when it emerges into realspace.
• Warp Coral is made up of crystals of (typically) lurid pink with flesh coloured veins. It leeches metals and other minerals out of its surroundings, concentrating them in its own crystals which can easily be collected and processed. The leeching process leaves the surroundings depleted, however, leaving the ground underneath effectively useless for agriculture and metals fatigued and brittle. When viewed by anyone with the ability to perceive the warp (Psykers, navigators, beings from Footfall etc..) a dense, thrumming energy can be detected within the individual crystals.
• The crystals of warp coral are like the shells of mollusks the dense thrumming energy is the actual creature. When observed psychically they can be seen to exude energy tendrils into their surroundings and withdraw them like an anemone feeding. Observing this requires close study and a -X (40 perhaps) psyniscience test.
• In real space living Warp Coral appears as manhole-sized lumps of rock or soil. As these lumps expand, the top of the lump pulls away, to reveal dense patches of crystal formations. As the patch of Warp Coral grows, both the lump of rock and crystal grow rapidly. The typical Warp Coral crystal is roughly 1 to 2 centimetres tall. The colour of the crystals is dependent on the amount and concentration of minerals that the Coral has leeched from the surroundings. Warp Coral can spread almost anywhere, with the rate of spread being influenced primarily by ambient temperature. Only excessive cold seems to prevent crystal growth. In real space Warp Coral can only grow into a small reef, maximum size 1-2 metres however isolated patches or even indi vidual crystals will eventually become a reef through a process that is not entirely understood but it is believed that underneath the surface, the rock lump shoots out tendrils in all directions, which grow into new rock lumps which eventually merge with the existing rock lumps.
• Warp Coral can be purged of the creature leaving empty white crystals. These crystals act as psyfoci but have no real other function. However they are adequate lenses/prisms if shaped.
• The Egarians used purged Warp Coral in the experiments that turned them into the Yu’Vath as the purged Warp Coral was compatible with the technology based on their own bio-luminescence. (Egarian/Yu'Vath history shamelessly stolen from Erathia)
• Corrupted Warp Coral (the sort the Egarian/Yu'Vath's used) is purple.
• Living Warp Coral can be used as a psyfocus. If it is any demonic result on the Perils of the Warp tables is replaced by the psyker gains 2d5 insanity points.
• Living Warp Coral can be forged into an edged weapon treat exactly as an Egarian Crystal blade except the blade has the holy quality and if it shatters then the wielder suffers 2d5 insanity points as the shards that pierce his skin shred his mind.
• Living Warp Coral can be ground up into a powder and applied to wounds. If it is used in this way the powder grows into the wound, forcibly
  holding the patient's collapsing form together and eroding their sanity. This heals 1d5 critical damage and gives the patient double that amount of insanity points.
• Living Warp Coral reefs can be installed as an upgrade on a ship (they do not take up enough space on the ship to be a component) Navigators may gaze into the crystals to get a safer journey. If they choose to do so they gain 2d5 insanity points and may reduce the number rolled on the warp encounter table by double the amount of insanity points they gained.
• When someone gains insanity due to living Warp Coral there is a chance that the Coral will induce a nascent Enslaver in that person (or three nascent Enslavers if the person is a psyker or a Navigator).
• The chance for Enslaver induction is equal to the number of insanity points the target has.
• Non-psykers/Non-Navigators may only ever host one nascent Enslaver, Navigators can host up to three nascent Enslavers and Psykers can host up to three nascent Enslavers per Psi Point.
• Nascent Enslavers need to mature before they can take control of their host. While they are immature they grant the host the Strong Minded, Pure Faith and Purge the Unclean Talents.
• A host of nascent Enslavers gains double Insanity points.
• A host of nascent Enslavers tends to gain madnesses that centre around obsession and paranoia.
• When a host of nascent Enslavers gets to 100 insanity points the Enslavers mature and take control of the character.
• When a host of mature Enslavers is killed the Enslavers emerge (though they can choose to emerge at any time after they have matured)
• Nascent and Mature Enslavers are very difficult to detect (Hellish Psynicience test).

And that is where I run out of steam.

Enslaver rules apparently exist in Deathwatch but I don't have that book.

The idea is that Enslavers work to create portals to gate in more Enslavers and then once there is some sort of critical mass the Enslavers fuse into Flying Polyps but without stats for Enslavers I have trouble working out how things progress.

Still here is a picture of an Enslaver and a warp gate made from an unwilling psyker

Ooooo....nice...and fits in with Erathia's account of the Egarians and Yu'Vath. I'm swiping it for my current campaign.

And Allaseo, no, not the Cthonians. C'thalpa, I think.

Cool if you make (or already have) stats for the Enslavers and/or Flying Polyps then post them. it'd be sweet to have the life cycle completed.

I've seen something on Enslavers somewhere. I'll try to look for it later.

Dark Heresy Creatures Anathema pg. 88.

I use Mindflayers from D&D as humans from the far future who use Myths-inspired bio-tech-symbiotic "flesh suits" (i.e. the whole mind flayer skin and head is in fact a suit) - of that they are the descendant worshipers of Cthulhu! (enter in here = muhahahha).

Its something I would if ever only run once a campaign - unless the players took an avid interest and sought it out with purpose.

**** pseudopods!

Morbid

Dark Heresy Creatures Anathema pg. 88.

Another book I don't have

However here are some images of the Flying Polyps.

**** Grot - those are some nice Minis (am jealous)...

Anyways back to Mindflayers - give em a Spelljammer (i.e. space ship) - then watch ypur players scratch their heads trying to figure out what exactly they are dealing with...

- no detectable power source sir, what is it?

They're not mine. They're from the boardgame that inspired me to put Flying Polyps into the game.

It is called Cthulhu Wars.