http://www.fanfiction.net/s/5840768/1/DarkeningSkies Halo x Cthulhu mythos, rated T

Some haloverse OCs fight a planet full of cultists, and later, some of the more powerful mythos entities. Including Azathoth, whose appearance in our space would mark the end of the universe. Azathoth has also gained Tsathoggua's formless spawn with no reason given. There are also several issues with said powerful mythos entities supporting their enemies and not supporting their allies.

<a href="http://www.fanfiction.net/s/7489360/1/TheDivineHorcrux">http://www.fanfiction.net/s/7489360/1/TheDivine_Horcrux Harry Potter x Cthulhu mythos, rated M

Voldemort is now a cultist, and decided to have Cthulhu be one of his horcruxes. Cthulhu is OOC and incorrectly called an "Elder god", can somehow teleport people directly to R'lyeh despite the city still being sunken AND is totally omniscient. There are also unexplained time jumps, uncanon methods of creating horcruxes, and has Hermoine gain huge amounts of knowledge regarding various mythos beasts that is supposed to be secret.