The Moon Presence AKA the Blood Moon AKA Formless Oedon AKA Formless Mother AKA Flora is based on Nyarlathotep.
He/She(Gods are confirmed in Elden Ring to have multiple genders as seen with Queen Marika and her “consort” Radagon who is just her in a different form) is behind the Healing Blood which his followers use. Those who imbibe the Healing Blood become Ghouls(Lovecraft’s version of Werewolves) due to the curse by the Worshippers of Kos for the first imbibers of Healing Blood killing Kos.
Kos has ties to the Cosmos incidentally according to Micolash(someone trying to get Eyes on his Brain from Kos). The Cosmos seems to be the Full Moon’s Domain and Ranni summons Ghostly Wolves in battle so Kos’s followers cursing those who use the Healing Blood is clearly the Full Moon’s attack on the Blood Moon.
One of the Blood Moon’s identities is Flora which explains why one of the Blood Magic Attacks has Plant-like Thorns involved. Starting to look like the Scarlet Rot is also of the Blood Moon…
Blood/Plants, Cosmos, the Void, Frenzied Flame(who apparently infected Laurence judging from his appearance) and Golden Stars… 5 Outer Gods…
Nyarlathotep is obvious(Blood/Plants) but which of the remaining 4 powers represents Yog-Sothoth, Shub-Niggurath and Azathoth?
Ah! but you seek Blood Gods not just the Blood God of Bloodborne yes? G’huun and Hakkar are Blood Gods!
G’huun like the Moon Presence combines Blood and Rot together while Hakkar just uses Blood…
The only Blood Gods besides these is Khorne as you have stated… Khorne demands Worthy Skulls! The Skulls of the Dishonorable! If you fight well and with Honor your Skull will be Unworthy and be left untaken. Offering an Honorable Skull(a big no no) will get you stuffed into his Forge because your Skull was Worthy of Burning!
You can guess that Worthy Skull means Worthy of Death rather than Worthy Opponent! The Skull Throne is for the Skulls of those Worthy of Death to be placed as a warning.
Khorne’s followers take each other’s Skulls so you can tell how much Khorne despises his followers! His Champion the Skulltaker uses Magic which Khorne hates by the way so he clearly wants his Skull offered to Khorne on a regular basis! He allows Skulltaker to reform immediately so that someone can kill him again and again as catharsis!
Skulltaker was resurrected multiple times as a reoccurring Boss of Warhammer 40K Inquisitor: Martyr and even resurrected thrice in one Mission! That’s how angry Skulltaker angered Khorne with his flagrant use of Magic!
Nurgle’s Greater Daemons according to Total War 3 are considered Honorable in comparison to everyone else in Khorne’s mind and thus are unlikely to have their Skulls taken(Skarbrand even states this as a reason to not take Kugath’s Skull if you decide to be diplomatic with him). Someone using a Disease(Nurgle’s method of doing things) to kill a bunch of people in Khorne’s name got ascended to a Daemon Prince of Khorne incidentally.