As J. P. has noted, Lovecraft's own conception of these things varied over time, and he also adapted certain things to the needs of a particular story. He was much, much less interested in the codifying aspect, as he felt that went against the entire idea of a genuine myth-cycle -- most such have numerous variant versions of even the primary stories -- just as fairy-tales, while often strikingly similar in basic outline and motifs, nonetheless present wide divergences in important aspects, even when coming from the same original source. (If you want a good example of the latter, go through Andrew Lang's Fairy Tale Books of Many Colors, and you'll see plenty of instances of this.)
But in Lovecraft's work, it is seldom that these entities are actually interested in gaining control of our world (much less us), as both are simply negligible in the overall scheme of things. We just aren't that important, and neither is our little flyspeck of a planet. The encounters are where we just happen to be in the way, or stumble across some evidence of their existence; in which case, if we become a nuisance, we are treated accordingly... but most often they simply don't even take note of our existence. (Their servitors, such as the Deep Ones, however, are another matter entirely. They are themselves either products of this planet's evolutionary diversity, or are on about the same plane as we as far as importance goes -- though usually considerably more powerful. And we can be of interest to them; though again it is strictly for their own ends, not anything intrinsically interesting in us.)
As for some of the other points you raise:
1. In "The Dunwich Horror", Wilbur and his family have goat like chins.
Actually, more a goatish appearance overall. The chins are receding chins, almost nonexistent.
2. In "The Shadow Over Innsmouth", some of the frog like fish were human converts.
These were the product of cross-breeding between the species; again, Lovecraft's take on miscegenation appearing.
3. In "Rats in the Walls" there is talk of hogs or pigs that were maybe human. I read that story a couple months ago, but the point is made.
Not hogs or pigs, but humans who had been debased to such an animalistic level for so long that it had affected their actual evolutionary development -- they had, as it would have been termed at the time, "devolved" back toward the primal state; a theme that is quite important in Lovecraft's work: see, for instance, "Innsmouth", "The Facts Concerning the Late Arthur Jermyn and His Family", the denizens of Dunwich, the strange hermit in "The Picture in the House", Joe Slater and his tribe in "Beyond the Wall of Sleep", etc.
What I see is witchcraft in the Dunwich story. They called the one character, a wizard, and than there is what appears to be animal sacrifice, and human blood being used.
There isn't any actual animal sacrifice here -- you simply have Wilbur's brother's appetite as he continues to grow at an almost exponential rate. Ditto for the human blood. As for witchcraft... that's a possibility, but debatable; at least in the "classical" sense of the term. The rituals certainly resemble "black magic" one sees in most horror tales featuring such, but there is reason to question whether it is actually magic or a very alien type of science... something which has been raised over the years by various commentators. A way of opening portals by use of sound and thought... and (as Lovecraft indicates in "The Dreams in the Witch House") perhaps the origin of our ideas of magic itself.
On the other hand, in the Innsmouth story the inhabitance are cross breeds that turn as they age, yet you have uncle Douglas who begins life as a human and has no choice, and others that are outside the cult that did not accept all of the oaths (1st, 2nd, 3rd), but there isn't any witchcraft in the Innsmouth story. [/quote]
Douglas (as with the narrator himself) was the descendant of one of the cultists who had so cross-bred. It is a matter of heredity, of genetics, at that point. So no, he would have no choice. What makes this both so horrible and so pitiful is that he would have no knowledge of this; thus the effects of such a change would be terrifying to him in the extreme, as well as likely to cause mental aberrations as he attempts to retain his humanity against the call of nature. And no, there is no witchcraft as such in the story, but there is that summoning of the Deep Ones via the golden object thrown into the water, and the cult's worship of Dagon, Mother Hydra, and Cthulhu, all of which have magical (or witchcraft) trappings.
I will try to get my hands on that author's book which when I looked it up returned "The Quest for Cthulhu". It said that August Derlith was a contemporary of Lovecraft. That is than a necessary book.
The Quest for Cthulhu is actually a republication, in combined form, of two earlier Derleth volumes:
The Mask of Cthulhu and
The Trail of Cthulhu (the latter an episodic novel combining Lovecraftian -- or Derlethian -- Mythos and the psychic detective type of tale). To be frank, it isn't very good, though (as J. P. notes), it can be entertaining; and it certainly did a good deal of the "codifying" of the Mythos mentioned above... along with Derleth's
The Lurker at the Threshold (probably his best contribution to the Mythos), etc. If you are approaching the whole thing from a gaming perspective, then it might be of use to you. If you want to get the real picture of Lovecraft's Mythos, avoid Derleth until you've read the whole of Lovecraft. Once you get Derleth's simplistic "good-evil"/"Old Ones-Elder Gods" schema in your head, it takes a lot of doing to get it out... it took nearly 35 years for that view to be challenged properly, and most people still see Lovecraft through Derleth-colored lenses. The two
ain't the same thing. They're about as far away from each other as two writers who knew each other could be.
If there isn't much more said about this subject than there seems to be a void in this subject that is prevalent, and I have many stories left, yet it is already evident that there is more than one form or shape of evil.
As noted above, these are themes that run through a good deal of Lovecraft's work, so there is actually quite a bit more to be said about them. The "transformations" aren't always the same sorts of things (De la Poer's "transformation" was not physical, for instance, but he nonetheless descended that evolutionary ladder as certainly as did any of the "flabby fungous beasts" kept as fodder by his ancestors, and in drastically less time; while Nathaniel Wingate Peaslee has his own "transformation" into a member of the Great Race when he finds his intellect trapped in the body of the being who has, in turn, taken over his own corporeal form; Randolph Carter, in his quest for his land of dreams, finds himself in the body of Zkauba, a
very alien wizard from a distant time and world who is, nonetheless, a very distant version of himself; and so on), but they are quite frequently there.