In need of something out of pure nightmare, ideas? (or own homebrew)

[Xeram]

Hello everyone.

After the end of a playtest dungeon's boss encounter, (a cult to Yog-Sothoth) Evil McGuffin artifact is about to get sundered.
Team dropped from 6 to 4.

This will release something horrible, as an alternative to thoroughly burying it for nobody to find.

I've browsed around, but haven't found something in the range of CR 9 that has peaked my interest.

Are there any juicy [outright disturbing/outer space/lovecraftian] monsters that would make a memorable final fight for 4 (lvl 7) PCs, in the d20 systems?

If anyone has homebrewed suggestions, i'm very much all ears.

Thanks.

[Pizza Lord]

I could probably come up with a pregnant, deepspawn-like creature that has a female, humanoid shape (like a moist, gray-skinned and flabby hag) that births fetal abominations. Then the umbilical cords detach from the mother and try to strike a character, every round draining blood and giving the fetal pods the target's appearance (or a vague semblance, they'd still be covered in amniotic goo or something and be naked, with grotesque traits). Meanwhile, the mother-spawn extrudes more umbilical cords that catch and draw targets into her 'nether maw', grinding them up with concealed rows of teeth and such, while her mammary glands drip a trail of sizzling black liquid down her distended and flabby belly onto the floor.

But, if you want something that already exists... I got nothing.

[avr]

CR +2 doesn't sound like an end boss for a competently built and played 4-member party. Maybe look a little higher? Also remember templates exist, adding class levels is allowed for most, and mooks help.

A color out of space with a few weak colour-blighted creatures could be terrifying, or a fungus queen with fungoid minions similarly.

Or perhaps a mi-go with levels in aberrant aegis and the tortured creatures it has experimented on.

[maouse33]

What? You're not going to follow Paizo's model and make them fight a Colossal Animated Object possessed by a Barbed Devil? It's just CR +4, one or two times...