These mostly look OK. Three thoughts straight away, though:
Cthulhu Larva reduces maximum stamina by 1, but doesn't give you a token or a marker or any way of remembering that. (Neither does Cthulhu Himself, but at least He stays next to the board, whereas this little guy will be going back in the cup sooner or later).
Cyborg is fine, but why is it treated as a cultist? Isn't that going to make it easier under some AOs?
Electric Succubus: sorry to be pedantic, but shouldn't it be "nearest street or location containing AN investigator" (singular, rather than plural)? Otherwise, it could be interpreted as only going after streets or locations which contain multiple investigators...
Mechanical Monsters - physical immunity and FOUR toughness? There's no definite reason why you can't do that, but are you sure you want to? No-one is going to want to go near the thing.