The Loch Ness Monster is really just a Kelpie that shapeshifts into a sea serpent when it wants to. Before the legend of Nessie became popular, a kelpie was what people originally believed lived in Loch Ness.
Not to mention the only record of a Chimera being killed "led to the unlucky wizard in question falling from his winged horse".note In the original legend, after slaying it while riding the winged horse Pegasus, Bellerophon tried to fly to Mount Olympus (where the gods lived). Guess how well that turned out for him.
The names of the winged horse breeds are taken from the names of mythical horses:
Abraxan and Aethonian: From Abraxus and Aethon, the horses that pulled the chariot of Helios, the Greek sun god
Granian: from Grani, the steed of Sigurd in the Volsunga Saga, and a descendant of Sleipnir.
Thestral: "Thester", an archaic English word that means, well, dark. So OK not all of them.
The Nundu, which resembles a Leopard — said to be utterly silent, gigantic, and able to wipe out entire villages just by breathing due to the diseases on its breath; it's so dangerous that the only successful kills have come from one hundred wizards working in concert. For comparison, that's ten times as many wizards as it takes to subdue the average dragon.
The Lethifold sneaks up on unsuspecting victims and smothers them in their sleep. And digests them on the spot and leaves no evidence of their demise. They also have a deceptive cunning to boot, that coupled with the fact that they can blend in with a fairly large range of things, means that they could be anywhere.
The Manticore, a Shout-Out to classical Greek Mythology. It has a man's head, a lion's body, and a scorpion's tail, and its sting causes instant death. If that wasn't enough, its skin is nigh-invulnerable to magic. Not to mention it can speak intelligently and croons while it eats its prey. And Hagrid possibly crossbred one.note It's a Rita Skeeter article, so take it with a grain of salt, but if anyone would crossbreed manticores with fire-crabs, it'd be Hagrid.
Then there's the Quintapeds. According to legend they were once a family of wizards before they were transformed into monsters by a rival wizard family, who were in turn eaten by the beasts they created. Whether or not the legend is true, these five-legged carnivorous beasts rate five Xs, and are so dangerous the island they live on has been marked completely hazardous and enchanted so it can't be placed on maps. God help us all if those things are capable of breeding.
The film series:
Broken Base: The upcoming film adaptation. While some are excited, others are accusing it of being a cash-grab.
Several long-time fans have taken issue with the lack of diversity in the casting choices of the main characters, especially since the film is not based on a book. Others have insisted that it isn't really that much of an issue because of the varied background characters in the trailer.
One point of excitement is that we're finally being given an opportunity to see the rest of the world, not bound to the Trio and Voldemort's story. Others have been a little more skeptical, and want the movie to take place in different locations around the world.
One rather sticky point of contention is the announcement that American wizards do not use the term Muggles, instead opting for "No-Maj". Some fans are far too devoted to the word "Muggle" to accept this. Others think that "Muggle" is such a British-sounding word that it makes perfect sense that it wouldn't be used overseas. Still others agree with the latter point but think that "No-Maj" is a weak alternative.
The fact that this is yet another prequel trilogy to a beloved franchise, especially coming off the heels of the highly divisive Star Wars prequels and the equally-received The Hobbit films. Some say that the new movies will follow in the same path as the aforementioned trilogies while others say to wait and see, as this won't directly tie into the Harry Potter films as much as what the previous prequel trilogies did to their respective franchise.
Fridge Horror: To anyone caught up on the Harry Potter books, the origin of the Scourers at first makes no sense, given we were told in an earlier book that the tragedy of the Witch Hunts, from actual wizard perspectives, is that they only killed Muggles, as actual wizards could easily get out of the mess with their magic. To the point mention is made of one Nightmare Fetishist witch who repeatedly got herself caught and burned because she enjoyed the sensation of flames under a Fire-Freezing Spell so much. The realization, and the dawning horror, is that the book was likely referring to the European Witch Hunts, which was purely an outburst of Muggle insanity and callous profiteering (see: the Witch Finder General). In America's Salem Witch Hunts, however, the whole affair was orchestrated by wizards, so those wizards and witches who got caught were probably attacked and rendered helpless by their own people first.