Part one here. Only a few entries this time, since I'm slaving away on the Dracula Dossier.
FLYING POLYP: Sometimes people just get these polyps, you know? They just sort of show up out of nowhere. They might be caused by a viral infection running rampant in someone with a compromised immune system, or just one of those funguses we have on us already suddenly proliferating. It's not weird or anything. Except when they whistle.
FOSTERLINGS OF THE OLD ONES: Already covered.
FUNGUS, VILE: Already covered.
GHASTS: One of the several sub-species of hominid created by the Serpent-Men, ghast-human hybrids no doubt occur in both nature and the laboratory, some new large, hairy, sneaky humanoid to to complicate the next season of Finding Bigfoot.
GHOULS: Already covered, in more ways than one.
GLAAKI, SERVANTS OF: Already covered.
GN'ICHT' TYAACHT: A certain thickness to the skin, a kind of barklike stiffness and thin, reedy hairs might single someone out as the child of a woman ravished by a tree spirit, or one whose child gestated within reach of one of their groves.
GNOPH-KEH: Already covered, maybe? This is a place where shape-shifting is a survival strategy, and the gnoph-keh as chimeric hybrid of bear, whale and Rhan-Tegoth might be a common kind of regal form some lost culture's sorcerers to take.
GOATSWOOD GNOMES: See Statue, Animated.
GOF'NN HUPADGH SHUB-NIGGURATH: Already covered.
GREEN ABYSS, SPAWN OF: See Boats of the Glen Carrig
GREEN GOD, CHILDREN OF THE: See The Pale Lady
GUGS: Worse than a hairlip, the jaw seems to have misgrown sideways, and the molars are wholly undeveloped. Muscles seem to be attached to anchor-points on the skull almost randomly. Another growth seems to be a vestigal arm growing backwards out of the elbow. Also, normally, we'd be in a position to perform a DNA test on the child to determine which worker in the coma ward impregnated his mother, but all the results come back as tainted samples. It's quite a mystery.